qemu: add udp interface support

qemu: add udp interface support

Adds a new interface type using UDP sockets, this seems only applicable
to QEMU but have edited tree-wide to support the new interface type.

The interface type required the addition of a "localaddr" (local
address), this then maps into the following xml and qemu call.

<interface type='udp'>
  <mac address='52:54:00:5c:67:56'/>
  <source address='127.0.0.1' port='11112'>
    <local address='127.0.0.1' port='22222'/>
  </source>
  <model type='virtio'/>
  <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
</interface>

QEMU call:
	-net socket,udp=127.0.0.1:11112,localaddr=127.0.0.1:22222

Notice the xml "local" entry becomes the "localaddr" for the qemu call.

reference:
http://lists.gnu.org/archive/html/qemu-devel/2011-11/msg00629.html

Signed-off-by: Jonathan Toppins <jtoppins@cumulusnetworks.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>