mac80211: support reporting 0-length PSDU in radiotap

For certain sounding frames, it may be useful to report them
to userspace even though they don't have a PSDU in order to
determine the PHY parameters (e.g. VHT rate/stream config.)
Add support for this to mac80211.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
diff --git a/include/net/ieee80211_radiotap.h b/include/net/ieee80211_radiotap.h
index 80d5439..8014153 100644
--- a/include/net/ieee80211_radiotap.h
+++ b/include/net/ieee80211_radiotap.h
@@ -75,6 +75,7 @@ enum ieee80211_radiotap_presence {
 	IEEE80211_RADIOTAP_TIMESTAMP = 22,
 	IEEE80211_RADIOTAP_HE = 23,
 	IEEE80211_RADIOTAP_HE_MU = 24,
+	IEEE80211_RADIOTAP_ZERO_LEN_PSDU = 26,
 	IEEE80211_RADIOTAP_LSIG = 27,
 
 	/* valid in every it_present bitmap, even vendor namespaces */
@@ -340,6 +341,11 @@ struct ieee80211_radiotap_lsig {
 	__le16 data1, data2;
 };
 
+enum ieee80211_radiotap_zero_len_psdu_type {
+	IEEE80211_RADIOTAP_ZERO_LEN_PSDU_SOUNDING		= 0,
+	IEEE80211_RADIOTAP_ZERO_LEN_PSDU_VENDOR			= 0xff,
+};
+
 /**
  * ieee80211_get_radiotap_len - get radiotap header length
  */