gue: Receive side for Generic UDP Encapsulation

This patch adds support receiving for GUE packets in the fou module. The
fou module now supports direct foo-over-udp (no encapsulation header)
and GUE. To support this a type parameter is added to the fou netlink
parameters.

For a GUE socket we define gue_udp_recv, gue_gro_receive, and
gue_gro_complete to handle the specifics of the GUE protocol. Most
of the code to manage and configure sockets is common with the fou.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/fou.h

@@ -13,6 +13,7 @@ enum {
 	FOU_ATTR_PORT,				/* u16 */
 	FOU_ATTR_AF,				/* u8 */
 	FOU_ATTR_IPPROTO,			/* u8 */
+	FOU_ATTR_TYPE,				/* u8 */
 
 	__FOU_ATTR_MAX,
 };
@@ -27,6 +28,12 @@ enum {
 	__FOU_CMD_MAX,
 };
 
+enum {
+	FOU_ENCAP_UNSPEC,
+	FOU_ENCAP_DIRECT,
+	FOU_ENCAP_GUE,
+};
+
 #define FOU_CMD_MAX	(__FOU_CMD_MAX - 1)
 
 #endif /* _UAPI_LINUX_FOU_H */