ip_gre: Add support to collect tunnel metadata.

Following patch create new tunnel flag which enable
tunnel metadata collection on given device.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index ac35a28..94428fd 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -742,7 +742,7 @@
 			goto drop;
 		if (iptunnel_pull_header(skb, 0, tpi.proto))
 			goto drop;
-		return ip_tunnel_rcv(tunnel, skb, &tpi, log_ecn_error);
+		return ip_tunnel_rcv(tunnel, skb, &tpi, NULL, log_ecn_error);
 	}
 
 	return 1;