NET: net_namespace, fix lock imbalance

register_pernet_gen_subsys omits mutex_unlock in one fail path.
Fix it.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/net_namespace.c

@@ -341,8 +341,8 @@ again:
 	rv = register_pernet_operations(first_device, ops);
 	if (rv < 0)
 		ida_remove(&net_generic_ids, *id);
-	mutex_unlock(&net_mutex);
 out:
+	mutex_unlock(&net_mutex);
 	return rv;
 }
 EXPORT_SYMBOL_GPL(register_pernet_gen_subsys);