rtnetlink: unlock on error path in netlink_dump()

In c7ac8679 "rtnetlink: Compute and store minimum ifinfo dump
size", we moved the allocation under the lock so we need to unlock
on error path.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NDavid S. Miller <davem@conan.davemloft.net>

net/netlink/af_netlink.c

@@ -1676,7 +1676,7 @@ static int netlink_dump(struct sock *sk)
 
 	skb = sock_rmalloc(sk, alloc_size, 0, GFP_KERNEL);
 	if (!skb)
-		goto errout;
+		goto errout_skb;
 
 	len = cb->dump(skb, cb);
 
@@ -1716,7 +1716,6 @@ static int netlink_dump(struct sock *sk)
 errout_skb:
 	mutex_unlock(nlk->cb_mutex);
 	kfree_skb(skb);
-errout:
 	return err;
 }