conf: parse/format <teaming> subelement of <interface>

conf: parse/format <teaming> subelement of <interface>

The subelement <teaming> of <interface> devices is used to configure a
simple teaming association between two interfaces in a domain. Example:

  <interface type='bridge'>
    <source bridge='br0'/>
    <model type='virtio'/>
    <mac address='00:11:22:33:44:55'/>
    <alias name='ua-backup0'/>
    <teaming type='persistent'/>
  </interface>
  <interface type='hostdev'>
    <source>
      <address type='pci' bus='0x02' slot='0x10' function='0x4'/>
    </source>
    <mac address='00:11:22:33:44:55'/>
    <teaming type='transient' persistent='ua-backup0'/>
  </interface>

The interface with <teaming type='persistent'/> is assumed to always
be present, while the interface with type='transient' may be be
unplugged and later re-plugged; the persistent='blah' attribute (and
in the one currently available implementation, also the matching MAC
addresses) is what associates the two devices with each other. It is
up to the hypervisor and the guest network drivers to determine what
to do with this information.

Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>