virtio: invoke set_status callback on reset

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>
(cherry picked from commit e0c472d8c2795e523b0f9006dbe5bc22545c8300)