mac80211: fix timing for 5 MHz and 10 MHz channels

according to IEEE 802.11-2012 section 18, various timings change
when using 5 MHz and 10 MHz. Reflect this by using a "shift" when
calculating durations.

Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 5256297..7475a7a 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -862,8 +862,9 @@
 	mi->sta = sta;
 	mi->stats_update = jiffies;
 
-	ack_dur = ieee80211_frame_duration(sband->band, 10, 60, 1, 1);
-	mi->overhead = ieee80211_frame_duration(sband->band, 0, 60, 1, 1) + ack_dur;
+	ack_dur = ieee80211_frame_duration(sband->band, 10, 60, 1, 1, 0);
+	mi->overhead = ieee80211_frame_duration(sband->band, 0, 60, 1, 1, 0);
+	mi->overhead += ack_dur;
 	mi->overhead_rtscts = mi->overhead + 2 * ack_dur;
 
 	mi->avg_ampdu_len = MINSTREL_FRAC(1, 1);