tcp: add in_flight to tcp_skb_cb

Add in_flight (bytes in flight when packet was sent) field
to tx component of tcp_skb_cb and make it available to
congestion modules' pkts_acked() function through the
ack_sample function argument.

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/include/net/tcp.h b/include/net/tcp.h
index 0bcc70f..a79894b 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -767,6 +767,7 @@
 	union {
 		struct {
 			/* There is space for up to 20 bytes */
+			__u32 in_flight;/* Bytes in flight when packet sent */
 		} tx;   /* only used for outgoing skbs */
 		union {
 			struct inet_skb_parm	h4;
@@ -859,6 +860,7 @@
 struct ack_sample {
 	u32 pkts_acked;
 	s32 rtt_us;
+	u32 in_flight;
 };
 
 struct tcp_congestion_ops {