udp: split sk_hash into two u16 hashes

Union sk_hash with two u16 hashes for udp (no extra memory taken)

One 16 bits hash on (local port) value (the previous udp 'hash')

One 16 bits hash on (local address, local port) values, initialized
but not yet used. This second hash is using jenkin hash for better
distribution.

Because the 'port' is xored later, a partial hash is performed
on local address + net_hash_mix(net)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sock.h b/include/net/sock.h
index 55de3bd..827366b 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -109,6 +109,7 @@
  *	@skc_refcnt: reference count
  *	@skc_tx_queue_mapping: tx queue number for this connection
  *	@skc_hash: hash value used with various protocol lookup tables
+ *	@skc_u16hashes: two u16 hash values used by UDP lookup tables
  *	@skc_family: network address family
  *	@skc_state: Connection state
  *	@skc_reuse: %SO_REUSEADDR setting
@@ -131,7 +132,10 @@
 	atomic_t		skc_refcnt;
 	int			skc_tx_queue_mapping;
 
-	unsigned int		skc_hash;
+	union  {
+		unsigned int	skc_hash;
+		__u16		skc_u16hashes[2];
+	};
 	unsigned short		skc_family;
 	volatile unsigned char	skc_state;
 	unsigned char		skc_reuse;