tcp: use correct net ns in cookie_v4_check()

Its better to make a route lookup in appropriate namespace.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 5c24db4..9f6b222 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -347,7 +347,7 @@
 					       { .sport = th->dest,
 						 .dport = th->source } } };
 		security_req_classify_flow(req, &fl);
-		if (ip_route_output_key(&init_net, &rt, &fl)) {
+		if (ip_route_output_key(sock_net(sk), &rt, &fl)) {
 			reqsk_free(req);
 			goto out;
 		}