From: "Ilpo_Järvinen" <redacted>
Date: Mon, 30 Jul 2007 20:18:45 +0300 (EEST)

Actually, the ratehalving seems to work too well, as cwnd is
reduced on every second ACK even though the packets in flight
remains unchanged. Recoveries in a bidirectional flows suffer
quite badly because of this, both NewReno and SACK are affected.

After this patch, rate halving is performed for ACK only if
packets in flight was supposedly changed too.

Signed-off-by: Ilpo Järvinen <redacted>

This fix looks great, and I see no potential problems with
Reno after doing a bit of auditing.

Applied and I'll push to -stable too.