virtio-net: Maintain reverse cleanup order

To easily audit the code, better to keep the device stop()
sequence to be mirror of the device open() sequence.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>