net: failover: check register_netdevice_notifier() error in failover_init()

failover_init() ignores register_netdevice_notifier() errors and always
returns success, which can leave the failover module loaded without its
netdev notifier registered.

Return the notifier registration result directly so module initialization
fails when registration fails.

This is a future looking check, register_netdevice_notifier()
only fails on double registration or if the registered notifier
itself returns an error.

Signed-off-by: Minhong He <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

net/core/failover.c

@@ -302,9 +302,7 @@ EXPORT_SYMBOL_GPL(failover_unregister);
 static __init int
 failover_init(void)
 {
-	register_netdevice_notifier(&failover_notifier);
-
-	return 0;
+	return register_netdevice_notifier(&failover_notifier);
 }
 module_init(failover_init);