Please add support for configuring a VLAN tag in the domain XML for Open vSwitch virtualports.
I believe this is implemented in http://libvirt.org/git/?p=libvirt.git;a=commit;h=3f9274a524804f8aa59c811932dba56550c120a1 so feel free to close this bug.
Well, actually that patch just permits specifying a vlan in the configuration, but provides no backend support. vlan support for Open vSwitch requires this later patch (and a few other bugfix patches): http://libvirt.org/git/?p=libvirt.git;a=commit;h=7d2b91b86a814d8469fd3aed10cff264ccab70cf but yes, support for this feature has been pushed upstream, and is fully functional in libvirt-0.10.1.