[TCP]: Convert highest_sack to sk_buff to allow direct access

It is going to replace the sack fastpath hint quite soon... :-)

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index bac17c5..34acee6 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -332,8 +332,10 @@
 
 	struct tcp_sack_block_wire recv_sack_cache[4];
 
-	u32	highest_sack;	/* Start seq of globally highest revd SACK
-				 * (validity guaranteed only if sacked_out > 0) */
+	struct sk_buff *highest_sack;   /* highest skb with SACK received
+					 * (validity guaranteed only if
+					 * sacked_out > 0)
+					 */
 
 	/* from STCP, retrans queue hinting */
 	struct sk_buff* lost_skb_hint;