network: support Open vSwitch

network: support Open vSwitch

This patch allows libvirt to add interfaces to already
existing Open vSwitch bridges. The following syntax in
domain XML file can be used:

    <interface type='bridge'>
      <mac address='52:54:00:d0:3f:f2'/>
      <source bridge='ovsbr'/>
      <virtualport type='openvswitch'>
        <parameters interfaceid='921a80cd-e6de-5a2e-db9c-ab27f15a6e1d'/>
      </virtualport>
      <address type='pci' domain='0x0000' bus='0x00'
                          slot='0x03' function='0x0'/>
    </interface>

or if libvirt should auto-generate the interfaceid use
following syntax:

    <interface type='bridge'>
      <mac address='52:54:00:d0:3f:f2'/>
      <source bridge='ovsbr'/>
      <virtualport type='openvswitch'>
      </virtualport>
      <address type='pci' domain='0x0000' bus='0x00'
                          slot='0x03' function='0x0'/>
    </interface>

It is also possible to pass an optional profileid. To do that
use following syntax:

   <interface type='bridge'>
     <source bridge='ovsbr'/>
     <mac address='00:55:1a:65:a2:8d'/>
     <virtualport type='openvswitch'>
       <parameters interfaceid='921a80cd-e6de-5a2e-db9c-ab27f15a6e1d'
                   profileid='test-profile'/>
     </virtualport>
   </interface>

To create Open vSwitch bridge install Open vSwitch and
run the following command:

    ovs-vsctl add-br ovsbr