virtio: invoke set_status callback on reset

As status is set to 0 on reset, invoke the relevant callback. This makes
for a cleaner code in devices as they don't need to duplicate the code
in their reset routine, as well as excercises this path a little more.

In particular this makes it possible to unify
vhost-net handling code with the following patch.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio.c

@@ -458,6 +458,8 @@ void virtio_reset(void *opaque)
     VirtIODevice *vdev = opaque;
     int i;
 
+    virtio_set_status(vdev, 0);
+
     if (vdev->reset)
         vdev->reset(vdev);