ila: Don't use dest cache when gateway is set

If the gateway is set on an ILA route we don't need to bother with using
the destination cache in the ILA route. Translation does not change the
routing in this case so we can stick with orig_output in the lwstate
output function.

Tested: Ran netperf with and without gateway for LWT route.
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ila/ila_lwt.c

@@ -36,6 +36,7 @@ static inline struct ila_params *ila_params_lwtunnel(
 static int ila_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
 	struct dst_entry *orig_dst = skb_dst(skb);
+	struct rt6_info *rt = (struct rt6_info *)orig_dst;
 	struct ila_lwt *ilwt = ila_lwt_lwtunnel(orig_dst->lwtstate);
 	struct dst_entry *dst;
 	int err = -EINVAL;
@@ -46,6 +47,13 @@ static int ila_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 	ila_update_ipv6_locator(skb, ila_params_lwtunnel(orig_dst->lwtstate),
 				true);
 
+	if (rt->rt6i_flags & (RTF_GATEWAY | RTF_CACHE)) {
+		/* Already have a next hop address in route, no need for
+		 * dest cache route.
+		 */
+		return orig_dst->lwtstate->orig_output(net, sk, skb);
+	}
+
 	dst = dst_cache_get(&ilwt->dst_cache);
 	if (unlikely(!dst)) {
 		struct ipv6hdr *ip6h = ipv6_hdr(skb);