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/include/uapi/linux/if_tunnel.h b/include/uapi/linux/if_tunnel.h
index bd3cc11..af4de90 100644
--- a/include/uapi/linux/if_tunnel.h
+++ b/include/uapi/linux/if_tunnel.h
@@ -112,6 +112,7 @@
 	IFLA_GRE_ENCAP_FLAGS,
 	IFLA_GRE_ENCAP_SPORT,
 	IFLA_GRE_ENCAP_DPORT,
+	IFLA_GRE_COLLECT_METADATA,
 	__IFLA_GRE_MAX,
 };