ipv6: Don't drop cache route entry unless timer actually expired.

This is ipv6 variant of the commit 5e016cbf6.. ("ipv4: Don't drop
redirected route cache entry unless PTMU actually expired")
by Guenter Roeck <guenter.roeck@ericsson.com>.

Remove cache route entry in ipv6_negative_advice() only if
the timer is expired.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -890,12 +890,17 @@ static struct dst_entry *ip6_negative_advice(struct dst_entry *dst)
 	struct rt6_info *rt = (struct rt6_info *) dst;
 
 	if (rt) {
-		if (rt->rt6i_flags & RTF_CACHE)
-			ip6_del_rt(rt);
-		else
+		if (rt->rt6i_flags & RTF_CACHE) {
+			if (rt6_check_expired(rt)) {
+				ip6_del_rt(rt);
+				dst = NULL;
+			}
+		} else {
 			dst_release(dst);
+			dst = NULL;
+		}
 	}
-	return NULL;
+	return dst;
 }
 
 static void ip6_link_failure(struct sk_buff *skb)