vlan: Propagate NETDEV_NOTIFY_PEERS notifier

The NETDEV_NOTIFY_PEERS notifier indicates that a device moved to a

different physical link; this also applies to any VLAN devices on top
of it.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>