net: Add ->neigh_lookup() operation to dst_ops

In the future dst entries will be neigh-less.  In that environment we
need to have an easy transition point for current users of
dst->neighbour outside of the packet output fast path.

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dst.h

@@ -387,6 +387,11 @@ static inline void dst_confirm(struct dst_entry *dst)
 	}
 }
 
+static inline struct neighbour *dst_neigh_lookup(const struct dst_entry *dst, const void *daddr)
+{
+	return dst->ops->neigh_lookup(dst, daddr);
+}
+
 static inline void dst_link_failure(struct sk_buff *skb)
 {
 	struct dst_entry *dst = skb_dst(skb);