virtio: disable notifications again after poll succeeded

While AioContext is in polling mode virtqueue notifications are not
necessary.  Some device virtqueue handlers enable notifications.  Make
sure they stay disabled to avoid unnecessary vmexits.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Tested-by: NRichard Henderson <rth@twiddle.net>
Tested-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio.c

@@ -2126,6 +2126,9 @@ static bool virtio_queue_host_notifier_aio_poll(void *opaque)
     }
 
     virtio_queue_notify_aio_vq(vq);
+
+    /* In case the handler function re-enabled notifications */
+    virtio_queue_set_notification(vq, 0);
     return true;
 }