ifb: fix oops when loading the ifb failed

If __rtnl_link_register() return faild when loading the ifb, it will
take the wrong path and get oops, so fix it just like dummy.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ifb.c

@@ -291,13 +291,17 @@ static int __init ifb_init_module(void)
 
 	rtnl_lock();
 	err = __rtnl_link_register(&ifb_link_ops);
+	if (err < 0)
+		goto out;
 
 	for (i = 0; i < numifbs && !err; i++) {
 		err = ifb_init_one(i);
 		cond_resched();
 	}
 	if (err)
 		__rtnl_link_unregister(&ifb_link_ops);
+
+out:
 	rtnl_unlock();
 
 	return err;