ippool: Memory leak

When element was removed from the list, it was not freed.
wifi: Memory leak when tethering
gdbus: Remove proxies when client disconnects

Remove proxies and generate proxy_removed callbacks even when there are
no corresponding InterfaceRemoved signals.

This patch fixes having zombie gdbus proxy object when a server
disconnects without sending InterfaceRemoved signals. These objects
may interact with new server instances, for example, making
InterfaceAdded signals of new objects with the same name be filtered
out as duplicated, or staying allocated, but unused, if the new server
doesn't reuse the object paths. Note that as a side-effect, the
lifetime of a gdbus proxy becomes stricter: it lives at most for the
duration of a single connection to a single instance of a server
process.
session_policy_local: Call failed_create() with the real user pointer
session_policy_local: Add support for UID/GID only

In case the host system does not support SELinux or SELinux is not 
configured, we fallback to UID/UID support only.
session_policy_local: Don't look up hash tables using NULL key
inet: Add functions to setup fwmark to routing table
inet: Add function to setup default route to a routing table
inet: Add function to remove default route from a routing table

Factor out the common code into iproute_default_modify() as it
has been done for __connman_inet_add_fwmark_rule() and
__connman_inet_del_fwmark_rule().
netlink: Port ELL's version of netlink

It is time to have a common netlink code code for RTNL and also
for the upcoming NFACCT handling in the session core.

ELL provides a nice implementation for the netlink interface, so
let's port it over to use GLib and when ELL is ready to be used
we easily can start using it.
netlink: process_multi() should call handler on done

Reason beeing, that the upper layer has no clue when the last
message has been received and therefore is unable to free resources.
netlink-test: Add test program for netlink
shared: Add a copy of the nfnetlink_acct.h kernel header

NFACCT was released with kernel 3.2 . We like to be able to build
ConnMan also on older kernels. The drawback could be missing runtime
support for Sessions but that is better than not be able to run
the daemon at all.

Added the copyright statement and NFNL_SUBSYS_ACCT definition.
nfacct: Add NFACCT

Add NFACCT low level function.
netlink-test: Add NFACCT low level test
nfacct: Add __connman_nfacct_flush()

Add helper function for flushing all nfacct rules.
nfacct: Add helper function for managing several rules
session: Store creation related data into a struct

During the creation period we need to keep track of data
which is only needed during this period. Let's rename user_config
to creation_data and store all the necessary data there. This includes
the session pointer so that we don't have to pass two void pointers
around in the callbacks which we will intrudoce soon.
session: Flush all NFACCT rules on bootup
session: Add NFACCT rules per session

There are a few reserved ids for the policy routing table (0, 253, 254
and 255). Let's start the marker with 256 to avoid conflicts.