net: add dst_pending_confirm flag to skbuff

Add new skbuff flag to allow protocols to confirm neighbour.
When same struct dst_entry can be used for many different
neighbours we can not use it for pending confirmations.

Add sock_confirm_neigh() helper to confirm the neighbour and
use it for IPv4, IPv6 and VRF before dst_neigh_output.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 264fc15..630eafd 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -378,6 +378,7 @@
 	if (unlikely(!neigh))
 		neigh = __neigh_create(&nd_tbl, nexthop, dst->dev, false);
 	if (!IS_ERR(neigh)) {
+		sock_confirm_neigh(skb, neigh);
 		ret = dst_neigh_output(dst, neigh, skb);
 		rcu_read_unlock_bh();
 		return ret;
@@ -574,8 +575,10 @@
 	neigh = __ipv4_neigh_lookup_noref(dev, nexthop);
 	if (unlikely(!neigh))
 		neigh = __neigh_create(&arp_tbl, &nexthop, dev, false);
-	if (!IS_ERR(neigh))
+	if (!IS_ERR(neigh)) {
+		sock_confirm_neigh(skb, neigh);
 		ret = dst_neigh_output(dst, neigh, skb);
+	}
 
 	rcu_read_unlock_bh();
 err: