rtnetlink: unlock on error path in netlink_dump()

In c7ac8679bec939 "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: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0b92f7549..ca5276c5 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1676,7 +1676,7 @@
 
 	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 @@
 errout_skb:
 	mutex_unlock(nlk->cb_mutex);
 	kfree_skb(skb);
-errout:
 	return err;
 }