net: add confirm_neigh method to dst_ops

Add confirm_neigh method to dst_ops and use it from IPv4 and IPv6
to lookup and confirm the neighbour. Its usage via the new helper
dst_confirm_neigh() should be restricted to MSG_PROBE users for
performance reasons.

For XFRM prefer the last tunnel address, if present. With help
from Steffen Klassert.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
index 8a2b66d..c84b328 100644
--- a/include/net/dst_ops.h
+++ b/include/net/dst_ops.h
@@ -33,6 +33,8 @@ struct dst_ops {
 	struct neighbour *	(*neigh_lookup)(const struct dst_entry *dst,
 						struct sk_buff *skb,
 						const void *daddr);
+	void			(*confirm_neigh)(const struct dst_entry *dst,
+						 const void *daddr);
 
 	struct kmem_cache	*kmem_cachep;