A further fix for:

  https://bugzilla.redhat.com/show_bug.cgi?id=1113474

Since there is no possibility that any type of macvtap will work if
the parent physdev it's attached to is offline, we should bring the
physdev online at the same time as the macvtap. When taking the
macvtap offline, it's also necessary to take the physdev offline for
macvtap passthrough mode (because the physdev has the same MAC address
as the macvtap device, so could potentially cause problems with
misdirected packets during migration, as outlined in commits 829770
and 879c13). We can't set the physdev offline for other macvtap modes
1) because there may be other macvtap devices attached to the same
physdev (and/or the host itself may be using the device) in the other
modes whereas passthrough mode is exclusive to one macvtap at a time,
and 2) there's no practical reason to do so anyway.