af_netlink: drop_monitor/dropwatch friendly

Need to consume_skb() instead of kfree_skb() in netlink_dump() and
netlink_unicast_kernel() to avoid false dropwatch positives.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -154,6 +154,12 @@ static void netlink_destroy_callback(struct netlink_callback *cb)
 	kfree(cb);
 }
 
+static void netlink_consume_callback(struct netlink_callback *cb)
+{
+	consume_skb(cb->skb);
+	kfree(cb);
+}
+
 static void netlink_sock_destruct(struct sock *sk)
 {
 	struct netlink_sock *nlk = nlk_sk(sk);
@@ -902,8 +908,10 @@ static int netlink_unicast_kernel(struct sock *sk, struct sk_buff *skb)
 		ret = skb->len;
 		skb_set_owner_r(skb, sk);
 		nlk->netlink_rcv(skb);
+		consume_skb(skb);
+	} else {
+		kfree_skb(skb);
 	}
-	kfree_skb(skb);
 	sock_put(sk);
 	return ret;
 }
@@ -1728,7 +1736,7 @@ static int netlink_dump(struct sock *sk)
 	nlk->cb = NULL;
 	mutex_unlock(nlk->cb_mutex);
 
-	netlink_destroy_callback(cb);
+	netlink_consume_callback(cb);
 	return 0;
 
 errout_skb: