tcp: replace cnt & rtt with struct in pkts_acked()

Replace 2 arguments (cnt and rtt) in the congestion control modules'
pkts_acked() function with a struct. This will allow adding more
information without having to modify existing congestion control
modules (tcp_nv in particular needs bytes in flight when packet
was sent).

As proposed by Neal Cardwell in his comments to the tcp_nv patch.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
index c10732e..4b03a2e 100644
--- a/net/ipv4/tcp_westwood.c
+++ b/net/ipv4/tcp_westwood.c
@@ -99,12 +99,13 @@
  * Called after processing group of packets.
  * but all westwood needs is the last sample of srtt.
  */
-static void tcp_westwood_pkts_acked(struct sock *sk, u32 cnt, s32 rtt)
+static void tcp_westwood_pkts_acked(struct sock *sk,
+				    const struct ack_sample *sample)
 {
 	struct westwood *w = inet_csk_ca(sk);
 
-	if (rtt > 0)
-		w->rtt = usecs_to_jiffies(rtt);
+	if (sample->rtt_us > 0)
+		w->rtt = usecs_to_jiffies(sample->rtt_us);
 }
 
 /*