9p/trans_virtio: reset virtio device on remove

On device shutdown/removal, virtio drivers need to trigger a reset on
the device; if this is neglected, the virtio core will complain about
non-zero device status.

This patch resets the status when the 9p virtio driver is removed
from the system by calling vdev->config->reset on the virtio_device
to send a reset to the host virtio device.

Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>