net: Changes to ip_tunnel to support foo-over-udp encapsulation

This patch changes IP tunnel to support (secondary) encapsulation,
Foo-over-UDP. Changes include:

1) Adding tun_hlen as the tunnel header length, encap_hlen as the
   encapsulation header length, and hlen becomes the grand total
   of these.
2) Added common netlink define to support FOU encapsulation.
3) Routines to perform FOU encapsulation.

Signed-off-by: Tom Herbert <therbert@google.com>
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 3bce9e9..9fedca7 100644
--- a/include/uapi/linux/if_tunnel.h
+++ b/include/uapi/linux/if_tunnel.h
@@ -53,10 +53,22 @@
 	IFLA_IPTUN_6RD_RELAY_PREFIX,
 	IFLA_IPTUN_6RD_PREFIXLEN,
 	IFLA_IPTUN_6RD_RELAY_PREFIXLEN,
+	IFLA_IPTUN_ENCAP_TYPE,
+	IFLA_IPTUN_ENCAP_FLAGS,
+	IFLA_IPTUN_ENCAP_SPORT,
+	IFLA_IPTUN_ENCAP_DPORT,
 	__IFLA_IPTUN_MAX,
 };
 #define IFLA_IPTUN_MAX	(__IFLA_IPTUN_MAX - 1)
 
+enum tunnel_encap_types {
+	TUNNEL_ENCAP_NONE,
+	TUNNEL_ENCAP_FOU,
+};
+
+#define TUNNEL_ENCAP_FLAG_CSUM		(1<<0)
+#define TUNNEL_ENCAP_FLAG_CSUM6		(1<<1)
+
 /* SIT-mode i_flags */
 #define	SIT_ISATAP	0x0001