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>
diff --git a/include/net/gue.h b/include/net/gue.h
new file mode 100644
index 0000000..b6c3327
--- /dev/null
+++ b/include/net/gue.h
@@ -0,0 +1,23 @@
+#ifndef __NET_GUE_H
+#define __NET_GUE_H
+
+struct guehdr {
+	union {
+		struct {
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+			__u8	hlen:4,
+			version:4;
+#elif defined (__BIG_ENDIAN_BITFIELD)
+			__u8	version:4,
+				hlen:4;
+#else
+#error  "Please fix <asm/byteorder.h>"
+#endif
+			__u8    next_hdr;
+			__u16   flags;
+		};
+		__u32 word;
+	};
+};
+
+#endif