[PATCH] tcp: clarify comment for mdev_us in struct tcp_sock

[Ziran Zhang <zhangcoder@yeah.net>]

The existing comment for mdev_us says "medium deviation", but this
term is inaccurate. The field stores the "mean deviation" of RTT,
as originally defined in Van Jacobson's paper "Congestion
Avoidance and Control", and it is scaled by 4 (<< 2) in the Linux
implementation.

Update the comment to reflect the correct terminology and storage
format.

Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---
 include/linux/tcp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 8a6807082..6a8c77719 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -274,7 +274,7 @@ struct tcp_sock {
 	u32	write_seq;	/* Tail(+1) of data held in tcp send buffer */
 	u32	pushed_seq;	/* Last pushed seq, required to talk to windows */
 	u32	lsndtime;	/* timestamp of last sent data packet (for restart window) */
-	u32	mdev_us;	/* medium deviation			*/
+	u32	mdev_us;	/* mean deviation of RTT, scaled by 4 (<< 2) in usecs */
 	u32	rtt_seq;	/* sequence number to update rttvar	*/
 	u32	max_packets_out;  /* max packets_out in last window */
 	u32	cwnd_usage_seq;  /* right edge of cwnd usage tracking flight */
-- 
2.51.0