mac80211: reject software RSSI CQM with beacon filtering

When beacon filtering is enabled the mac80211 software implementation
for RSSI CQM cannot work as beacons will not be available. Rather than
accepting such a configuration without proper effect, reject it.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -2468,6 +2468,10 @@ static int ieee80211_set_cqm_rssi_config(struct wiphy *wiphy,
 	    rssi_hyst == bss_conf->cqm_rssi_hyst)
 		return 0;
 
+	if (sdata->vif.driver_flags & IEEE80211_VIF_BEACON_FILTER &&
+	    !(sdata->vif.driver_flags & IEEE80211_VIF_SUPPORTS_CQM_RSSI))
+		return -EOPNOTSUPP;
+
 	bss_conf->cqm_rssi_thold = rssi_thold;
 	bss_conf->cqm_rssi_hyst = rssi_hyst;