remove redundant material from setup.py

Commit d3fd6b84f461a4d7ffbf3f3eae37381150b69e82 introduced an ext_modules
keyword argument to the setup invocation in setup.py, making the

   exttool = Extension(...)

code at the top of setup.py redundant.  Remove the redundant code.
Fix buffer overflow in get_module()

get_module() includes this scanf call:

  if (sscanf(buf, "%*d\t%*s\t%100s\t%*d\t%100s\n", driver, dev) > 0) {

i.e. "%100s" for each of driver and dev.  i.e. a maximum field width of
100 for each.

However, this field width does not include the NUL terminator.

Increase the size of driver and dev from 100 to 101 to allow for the NUL byte.

This appears to have been present in the initial commit of the code
(8d6ad996f5d60d569532cdba4febb19c69bdf488)

Found by Braňo Náter using the "cppcheck" static analyzer.
Fix bad loop condition within get_devices()

get_devices() includes this loop:

     char buffer[256];

     ...snip...

     char *end = buffer;

     ...snip...

     while (end && *end != ':')
         end++;

The condition "end" within the while guard will always be true, given that
buffer is on the stack and thus will never be near the zero value.  It
should be *end instead, to check for the NUL terminator byte: this code
will likely crash if the string does not contain a colon character.

This appears to have been present in the initial commit of the code
(8d6ad996f5d60d569532cdba4febb19c69bdf488)

Found by Braňo Náter using the "cppcheck" static analyzer.
Fix memory leaks in get_interfaces_info()

The first half of get_interfaces_info() potentially allocates fetch_devs
using calloc, setting fetch_devs_len to a value which may or may not be
non-zero.

In particular, given a tuple argument containing all non-strings,
allocation occurs, but fetch_devs_len is set to zero, so it's not correct
to use (fetch_devs_len > 0) as the condition for freeing the memory on the
primary exit path, as this would leak fetch_devs (introduced in
bfdcac6b16806416a6c0295fcfad5d820595d88c)

There are also two error-handling paths that fail to free it (introduced in
4f0295fca2cfd933f4b9b539d5505cb24e4d420c)

Instead of this logic, simply initialize it to NULL, and pass it to free on
every exit route of the second half of the function: free(NULL) is
guaranteed to be a no-op.

Found by Braňo Náter using the "cppcheck" static analyzer.
Eliminate "ret" within _ethtool_etherinfo_getter

This variable was confusing cppcheck and potentially could
introduce a read of an uninitialized variable if the code
were carelessly modified - simplify it.
Support devices with multiple IPv4 addresses

Add a get_ipv4_addresses() method to ethtool.etherinfo to support devices
with multiple IPv4 addresses (rhbz#759150)

Previously, get_etherinfo() made queries to NETLINK with NLQRY_ADDR, and
callback_nl_address handled responses of family AF_INET (IPv4) by writing to
fields within a struct etherinfo.

If multiple AF_INET responses come back, each overwrote the last, and the
last one won.

This patch generalizes things by moving the relevant fields:
   char *ipv4_address;                 /**< Configured IPv4 address */
   int ipv4_netmask;                   /**< Configured IPv4 netmask */
   char *ipv4_broadcast;
from (struct etherinfo) into a new Python class, currently named
PyNetlinkIPv4Address.

This object has a sane repr():
>>> ethtool.get_interfaces_info('eth1')[0].get_ipv4_addresses()
[ethtool.NetlinkIPv4Address(address='192.168.1.10', netmask=24, broadcast='192.168.1.255')]

and attributes:
>>> print [iface.address for iface in ethtool.get_interfaces_info('eth1')[0].get_ipv4_addresses()]
['192.168.1.10']
>>> print [iface.netmask for iface in ethtool.get_interfaces_info('eth1')[0].get_ipv4_addresses()]
[24]
>>> print [iface.broadcast for iface in ethtool.get_interfaces_info('eth1')[0].get_ipv4_addresses()]
['192.168.1.255']

The (struct etherinfo) then gains a new field:
   PyObject *ipv4_addresses;        /**< list of PyNetlinkIPv4Address instances */

which is created before starting the query, and populated by the callback as
responses come in.

All direct usage of the old fields (which assumed a single IPv4 address)
are changed to use the last entry in the list (if any), to mimic the old
behavior.

dump_etherinfo() and _ethtool_etherinfo_str() are changed to loop over all
of the IPv4 addresses when outputting, rather than just outputting one.

Caveats:
* the exact terminology is probably incorrect: I'm not a networking
  specialist
* the relationship between each of devices, get_interfaces_info() results,
  and addresses seems both unclear and messy to me: how changable is the
  API?

>>> ethtool.get_interfaces_info('eth1')[0].get_ipv4_addresses()
[ethtool.NetlinkIPv4Address(address='192.168.1.10', netmask=24, broadcast='192.168.1.255')]

It seems that an etherinfo object relates to a device: perhaps it should be
named as such?  But it may be too late to make this change.

Notes:
The _ethtool_etherinfo_members array within python-ethtool/etherinfo_obj.c
was broken: it defined 4 attributes of type PyObject*, to be extracted from
etherinfo_py->data, which is of a completed different type.  If these
PyMemberDef fields were ever used, Python would segfault.  Thankfully
_ethtool_etherinfo_getter() has handlers for these attributes, and gets
called first.

This is a modified version of the patch applied downstream in RHEL 6.4
within python-ethtool-0.6-3.el6:
  python-ethtool-0.6-add-get_ipv4_addresses-method.patch
ported to take account of 508ffffbb3c48eeeb11eeab2bf971180fe4e1940
"char *devname" -> "const char *devname" throughout

Calling
   PyArg_ParseTuple(args, "s", &devname)
populates devname with a pointer to the internal storage of an
(supposedly) immutable string.

Make sure the buffer doesn't get mutated by making these pointers be
"const char *", rather than just "char *".

Found using cpychecker
add python-ethtool/netlink-address.c to MANIFEST

It's not clear to me that we need a handcoded MANIFEST file, but
if we're going to have it, it ought to be complete.
add a test suite

This is based on a suite I wrote internally at Red Hat for python-ethtool,
later modified by Braňo Náter <bnater@redhat.com>.
update URL within specfile to point to git.fedorahosted.org repo
bump version to 0.8
update "Source:" URL within specfile