net: In unregister_netdevice_notifier unregister the netdevices.

net: In unregister_netdevice_notifier unregister the netdevices.

[ Upstream commit 7d3d43dab4e978d8d9ad1acf8af15c9b1c4b0f0f ]

We already synthesize events in register_netdevice_notifier and synthesizing
events in unregister_netdevice_notifier allows to us remove the need for
special case cleanup code.

This change should be safe as it adds no new cases for existing callers
of unregiser_netdevice_notifier to handle.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>