gre: Add netlink interface

This patch adds a netlink interface that will eventually displace
the existing ioctl interface.  It utilises the elegant rtnl_link_ops
mechanism.

This also means that user-space no longer needs to rely on the
tunnel interface being of type GRE to identify GRE tunnels.  The
identification can now occur using rtnl_link_ops.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/if_tunnel.h b/include/linux/if_tunnel.h
index d4efe40..aeab2cb 100644
--- a/include/linux/if_tunnel.h
+++ b/include/linux/if_tunnel.h
@@ -2,6 +2,7 @@
 #define _IF_TUNNEL_H_
 
 #include <linux/types.h>
+#include <linux/ip.h>
 
 #define SIOCGETTUNNEL   (SIOCDEVPRIVATE + 0)
 #define SIOCADDTUNNEL   (SIOCDEVPRIVATE + 1)
@@ -47,4 +48,22 @@
 /* PRL flags */
 #define	PRL_DEFAULT		0x0001
 
+enum
+{
+	IFLA_GRE_UNSPEC,
+	IFLA_GRE_LINK,
+	IFLA_GRE_IFLAGS,
+	IFLA_GRE_OFLAGS,
+	IFLA_GRE_IKEY,
+	IFLA_GRE_OKEY,
+	IFLA_GRE_LOCAL,
+	IFLA_GRE_REMOTE,
+	IFLA_GRE_TTL,
+	IFLA_GRE_TOS,
+	IFLA_GRE_PMTUDISC,
+	__IFLA_GRE_MAX,
+};
+
+#define IFLA_GRE_MAX	(__IFLA_GRE_MAX - 1)
+
 #endif /* _IF_TUNNEL_H_ */