Actually use the new field of the used ring and tell the device if SVQ
wants to be notified.
The code is not reachable at the moment.
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>