mac80211: add support for MU-MIMO air sniffer

add support to MU-MIMO air sniffer according groupID:
in monitor mode, use a given MU-MIMO groupID to monitor stations
that belongs to that group using MU-MIMO.

add support for following a station according to its MAC address
using VHT MU-MIMO sniffer:
the monitors wait until they get an action MU-MIMO notification
frame, then parses it in order to find the groupID that corresponds
to the given MAC address and monitors packets destined to that
groupID using VHT MU-MIMO.

Signed-off-by: Aviya Erenfeld <aviya.erenfeld@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/iface.c

diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index c8509d9..b0abddc7 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -43,6 +43,8 @@
  * by either the RTNL, the iflist_mtx or RCU.
  */
 
+static void ieee80211_iface_work(struct work_struct *work);
+
 bool __ieee80211_recalc_txpower(struct ieee80211_sub_if_data *sdata)
 {
 	struct ieee80211_chanctx_conf *chanctx_conf;
@@ -448,6 +450,9 @@
 		return ret;
 	}
 
+	skb_queue_head_init(&sdata->skb_queue);
+	INIT_WORK(&sdata->work, ieee80211_iface_work);
+
 	return 0;
 }