ip6_gre: Add ERSPAN native tunnel support

The patch adds support for ERSPAN tunnel over ipv6.

Signed-off-by: William Tu <u9012063@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: williamtu

include/net/ip6_tunnel.h

@@ -36,6 +36,7 @@ struct __ip6_tnl_parm {
 	__be32			o_key;
 
 	__u32			fwmark;
+	__u32			index;	/* ERSPAN type II index */
 };
 
 /* IPv6 tunnel */