network: increase max number of routes

This fixes the problem reported in:

   https://bugzilla.redhat.com/show_bug.cgi?id=972690

When checking for a collision of a new libvirt network's subnet with
any existing routes, we read all of /proc/net/route into memory, then
parse all the entries. The function that we use to read this file
requires a "maximum length" parameter, which had previously been set
to 64*1024. As each line in /proc/net/route is 128 bytes, this would
allow for a maximum of 512 entries in the routing table.

This patch increases that number to 128 * 100000, which allows for
100,000 routing table entries. This means that it's possible that 12MB
would be allocated, but that would only happen if there really were
100,000 route table entries on the system, it's only held for a very
short time.

Since there is no method of specifying and unlimited max (and that
would create a potential denial of service anyway) hopefully this
limit is large enough to accomodate everyone.
build: Fix build with -Werror

Commit 752596b5 broke the build with -Werror

qemu/qemu_hotplug.c: In function 'qemuDomainChangeGraphics':
qemu/qemu_hotplug.c:1980:39: error: declaration of 'listen' shadows a
  global declaration [-Werror=shadow]

Fix with s/listen/newlisten/
qemu: Make probing for events declarative
qemu: Make probing for commands declarative
conf: Requires either uuid or usage of secret

As the RNG schema for disk auth secret implies, it requires either
"uuid" or "usage":

  <define name='diskAuthSecret'>
    <element name='secret'>
      <attribute name='type'>
        <choice>
          <value>ceph</value>
          <value>iscsi</value>
        </choice>
      </attribute>
      <choice>
        <attribute name='uuid'>
          <ref name="UUID"/>
        </attribute>
        <attribute name='usage'>
          <ref name='genericName'/>
        </attribute>
      </choice>
    </element>
  </define>
BSD: implement virNetDevBridgeCreate() and virNetDevBridgeDelete()

Implementation uses SIOCIFCREATE2 and SIOCIFDESTROY ioctls.
Also, drop static virNetDevSetupControl() as we have
public one avialable now.
BSD: implement bridge add/remove port and set STP
conf: add vapic and spinlocks to hyperv features

Add new CPU features for HyperV:
vapic for virtual APIC support
spinlocks for setting spinlock support

<features>
  <hyperv>
    <vapic state='on'/>
    <spinlocks state='on' retries='4096'/>
  </hyperv>
</features>

https://bugzilla.redhat.com/show_bug.cgi?id=784836
qemu: add hv_vapic and hv_spinlocks support

XML:
<features>
  <hyperv>
    <vapic state='on'/>
    <spinlocks state='on' retries='4096'/>
  </hyperv>
</features>

results in the following QEMU command line:
qemu -cpu <cpu_model>,hv_vapic,hv_spinlocks=0x1000

https://bugzilla.redhat.com/show_bug.cgi?id=784836
util: add support for qcow2v3 image detection

Detect qcow2 images with version 3 in the image header as
VIR_STORAGE_FILE_QCOW2.

These images have a feature bitfield, with just one feature supported
so far: lazy_refcounts.

The header length changed too, moving the location of the backing
format name.
conf: add features to volume target XML

Add <features> and <compat> elements to volume target XML.

<compat> is a string which for qcow2 represents the QEMU version
it should be compatible with. Valid values are 0.10 and 1.1.
1.1 is implicit if the <features> element is present, otherwise
qemu-img default is used. 0.10 can be specified to explicitly
create older images after the qemu-img default changes.

<features> contains optional features, so far
<lazy_refcounts/> is available, which enables caching of reference
counters, improving performance for snapshots.
storage: add support for creating qcow2 images with extensions

Add -o compat= and -o lazy_refcounts options for qemu-img.
libxl: Allow libxl to set NIC devid

libxl contains logic to determine an appropriate devid for new devices
that do not specify one in their configuration.  For all device types
except NICs, the libxl driver allows libxl to determine devid.  Do the
same for NICs.
libxl: Implement virConnectGetSysinfo

virConnectGetSysinfo was never implemented in the libxl driver.
This patch provides an implementation based on the qemu driver.
xen: Implement virConnectGetSysinfo

virConnectGetSysinfo was never implemented in the legacy xen driver.
This patch provides an implementation based on the qemu driver.
netdev: accept NULL in virNetDevSetupControl

Commit b9c6b073 dropped the version of virNetDevSetupControl
that didn't check for NULL arguments, but we call it like that
in virNetDevBridgeDelete.