mac80211: parse VHT info in injected frames

Add VHT radiotap parsing support to ieee80211_parse_tx_radiotap().
That capability has been tested using a d-link dir-860l rev b1 running
OpenWrt trunk and mt76 driver

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/Documentation/networking/mac80211-injection.txt b/Documentation/networking/mac80211-injection.txt
index ec8f934..e0efcaf 100644
--- a/Documentation/networking/mac80211-injection.txt
+++ b/Documentation/networking/mac80211-injection.txt
@@ -45,6 +45,19 @@
    number of retries when either IEEE80211_RADIOTAP_RATE or
    IEEE80211_RADIOTAP_MCS was used
 
+ * IEEE80211_RADIOTAP_VHT
+
+   VHT mcs and number of streams used in the transmission (only for devices
+   without own rate control). Also other fields are parsed
+
+   flags field
+   IEEE80211_RADIOTAP_VHT_FLAG_SGI: use short guard interval
+
+   bandwidth field
+   1: send using 40MHz channel width
+   4: send using 80MHz channel width
+   11: send using 160MHz channel width
+
 The injection code can also skip all other currently defined radiotap fields
 facilitating replay of captured radiotap headers directly.