udp: Add GRO functions to UDP socket

This patch adds GRO functions (gro_receive and gro_complete) to UDP
sockets. udp_gro_receive is changed to perform socket lookup on a
packet. If a socket is found the related GRO functions are called.

This features obsoletes using UDP offload infrastructure for GRO
(udp_offload). This has the advantage of not being limited to provide
offload on a per port basis, GRO is now applied to whatever individual
UDP sockets are bound to.  This also allows the possbility of
"application defined GRO"-- that is we can attach something like
a BPF program to a UDP socket to perfrom GRO on an application
layer protocol.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/udp.h b/include/linux/udp.h
index 3234275..d1fd8cd 100644
--- a/include/linux/udp.h
+++ b/include/linux/udp.h
@@ -71,6 +71,14 @@
 	 */
 	int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);
 	void (*encap_destroy)(struct sock *sk);
+
+	/* GRO functions for UDP socket */
+	struct sk_buff **	(*gro_receive)(struct sock *sk,
+					       struct sk_buff **head,
+					       struct sk_buff *skb);
+	int			(*gro_complete)(struct sock *sk,
+						struct sk_buff *skb,
+						int nhoff);
 };
 
 static inline struct udp_sock *udp_sk(const struct sock *sk)