https://bugzilla.redhat.com/show_bug.cgi?id=1484230

When updating a virtio enabled vNIC and trying to change either
of rx_queue_size or tx_queue_size success is reported although no
operation is actually performed. Moreover, there's no way how to
change these on the fly. This is due to way we check for changes:
explicitly for each struct member. Therefore it's easy to miss
one.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>