mac80211: Account HT Control field in Data frame hdrlen according to 802.11n-2009

ieee80211_hdrlen() should account account new HT Control field in 802.11
data frame header introduced by IEEE 802.11n standard.

According to 802.11n-2009 HT Control field is present in data frames
when both of following are met:

   1. It is QoS data frame.
   2. Order bit is set in Frame Control field.

The change might be totally compatible with legacy non-11n aware frames,
because 802.11-2007 standard states that "all QoS STAs set this subfield
to 0".
Signed-off-by: Andriy V. Tkachuk <andrit@ukr.net>
Acked-by : Benoit Papillault <benoit.papillault@free.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/linux/ieee80211.h

@@ -138,6 +138,8 @@
 #define IEEE80211_WMM_IE_STA_QOSINFO_SP_MASK	0x03
 #define IEEE80211_WMM_IE_STA_QOSINFO_SP_SHIFT	5
 
+#define IEEE80211_HT_CTL_LEN		4
+
 struct ieee80211_hdr {
 	__le16 frame_control;
 	__le16 duration_id;

net/wireless/util.c

@@ -227,8 +227,11 @@ unsigned int ieee80211_hdrlen(__le16 fc)
 	if (ieee80211_is_data(fc)) {
 		if (ieee80211_has_a4(fc))
 			hdrlen = 30;
-		if (ieee80211_is_data_qos(fc))
+		if (ieee80211_is_data_qos(fc)) {
 			hdrlen += IEEE80211_QOS_CTL_LEN;
+			if (ieee80211_has_order(fc))
+				hdrlen += IEEE80211_HT_CTL_LEN;
+		}
 		goto out;
 	}