net: add netnotifier event for upper device change

Now when upper device is changed, event is not propagated via RT Netlink
to userspace. Userspace might never now about the change. Fix this by
adding upper-device-change notifier event.
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1593,6 +1593,7 @@ struct packet_offload {
 #define NETDEV_RELEASE		0x0012
 #define NETDEV_NOTIFY_PEERS	0x0013
 #define NETDEV_JOIN		0x0014
+#define NETDEV_CHANGEUPPER	0x0015
 
 extern int register_netdevice_notifier(struct notifier_block *nb);
 extern int unregister_netdevice_notifier(struct notifier_block *nb);

net/core/dev.c

@@ -4411,7 +4411,7 @@ static int __netdev_upper_dev_link(struct net_device *dev,
 	else
 		list_add_tail_rcu(&upper->list, &dev->upper_dev_list);
 	dev_hold(upper_dev);
-
+	call_netdevice_notifiers(NETDEV_CHANGEUPPER, dev);
 	return 0;
 }
 
@@ -4471,6 +4471,7 @@ void netdev_upper_dev_unlink(struct net_device *dev,
 	list_del_rcu(&upper->list);
 	dev_put(upper_dev);
 	kfree_rcu(upper, rcu);
+	call_netdevice_notifiers(NETDEV_CHANGEUPPER, dev);
 }
 EXPORT_SYMBOL(netdev_upper_dev_unlink);