ipv6: Avoid redoing fib6_lookup() for RTF_CACHE hit case

When there is a RTF_CACHE hit, no need to redo fib6_lookup()
with reachable=0.

Cc: David Miller <davem@davemloft.net>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -944,12 +944,12 @@ redo_rt6_select:
 			goto out;
 	}
 
-	if (rt->rt6i_flags & RTF_CACHE)
-		goto out;
-
 	dst_hold(&rt->dst);
 	read_unlock_bh(&table->tb6_lock);
 
+	if (rt->rt6i_flags & RTF_CACHE)
+		goto out2;
+
 	if (!(rt->rt6i_flags & (RTF_NONEXTHOP | RTF_GATEWAY)))
 		nrt = rt6_alloc_cow(rt, &fl6->daddr, &fl6->saddr);
 	else if (!(rt->dst.flags & DST_HOST))