net: Drop NETDEV_UNREGISTER_FINAL

Last user is gone after bdf5bd7f2132 "rds: tcp: remove
register_netdevice_notifier infrastructure.", so we can
remove this netdevice command. This allows to delete
rtnl_lock() in netdev_run_todo(), which is hot path for
net namespace unregistration.

dev_change_net_namespace() and netdev_wait_allrefs()
have rcu_barrier() before NETDEV_UNREGISTER_FINAL call,
and the source commits say they were introduced to
delemit the call with NETDEV_UNREGISTER, but this patch
leaves them on the places, since they require additional
analysis, whether we need in them for something else.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index ff3ed43..6eb1747 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -2122,8 +2122,8 @@ struct ib_device {
 	 * net device of device @device at port @port_num or NULL if such
 	 * a net device doesn't exist. The vendor driver should call dev_hold
 	 * on this net device. The HW vendor's device driver must guarantee
-	 * that this function returns NULL before the net device reaches
-	 * NETDEV_UNREGISTER_FINAL state.
+	 * that this function returns NULL before the net device has finished
+	 * NETDEV_UNREGISTER state.
 	 */
 	struct net_device	  *(*get_netdev)(struct ib_device *device,
 						 u8 port_num);