qemu: Forbid rx/tx_queue_size change explicitly

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>

src/qemu/qemu_hotplug.c

@@ -3067,6 +3067,8 @@ qemuDomainChangeNet(virQEMUDriverPtr driver,
          olddev->driver.virtio.ioeventfd != newdev->driver.virtio.ioeventfd ||
          olddev->driver.virtio.event_idx != newdev->driver.virtio.event_idx ||
          olddev->driver.virtio.queues != newdev->driver.virtio.queues ||
+         olddev->driver.virtio.rx_queue_size != newdev->driver.virtio.rx_queue_size ||
+         olddev->driver.virtio.tx_queue_size != newdev->driver.virtio.tx_queue_size ||
          olddev->driver.virtio.host.csum != newdev->driver.virtio.host.csum ||
          olddev->driver.virtio.host.gso != newdev->driver.virtio.host.gso ||
          olddev->driver.virtio.host.tso4 != newdev->driver.virtio.host.tso4 ||