mac80211: fix crash on getting sta info with uninitialized rate control

If the expected throughput is queried before rate control has been
initialized, the minstrel op for it will crash while trying to access
the rate table.
Check for WLAN_STA_RATE_CONTROL before attempting to use the rate
control op.
Reported-by: NJean-Pierre Tosoni <jp.tosoni@acksys.fr>
Signed-off-by: NFelix Fietkau <nbd@openwrt.org>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -472,12 +472,15 @@ static void sta_set_sinfo(struct sta_info *sta, struct station_info *sinfo)
 {
 	struct ieee80211_sub_if_data *sdata = sta->sdata;
 	struct ieee80211_local *local = sdata->local;
-	struct rate_control_ref *ref = local->rate_ctrl;
+	struct rate_control_ref *ref = NULL;
 	struct timespec uptime;
 	u64 packets = 0;
 	u32 thr = 0;
 	int i, ac;
 
+	if (test_sta_flag(sta, WLAN_STA_RATE_CONTROL))
+		ref = local->rate_ctrl;
+
 	sinfo->generation = sdata->local->sta_generation;
 
 	sinfo->filled = STATION_INFO_INACTIVE_TIME |