rtnetlink: potential ERR_PTR dereference

In the original code, if rtnl_create_link() returned an ERR_PTR then that
would get passed to rtnl_configure_link() which dereferences it.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/rtnetlink.c

@@ -1270,10 +1270,11 @@ static int rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 			err = ops->newlink(net, dev, tb, data);
 		else
 			err = register_netdevice(dev);
-		if (err < 0 && !IS_ERR(dev)) {
+
+		if (err < 0 && !IS_ERR(dev))
 			free_netdev(dev);
+		if (err < 0)
 			goto out;
-		}
 
 		err = rtnl_configure_link(dev, ifm);
 		if (err < 0)