mac80211_hwsim: fix RCU protected chanctx access

We need to RCU protect the chanctx_conf access, so
do that.

Fixes: 585625c9 ("mac80211_hwsim: check TX and STA bandwidth")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20220505230421.fb8055c081a2.Ic6da3307c77a909bd61a0ea25dc2a4b08fe1b03f@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/mac80211_hwsim.c

@@ -2202,11 +2202,14 @@ mac80211_hwsim_sta_rc_update(struct ieee80211_hw *hw,
 	if (!data->use_chanctx) {
 		confbw = data->bw;
 	} else {
-		struct ieee80211_chanctx_conf *chanctx_conf =
-			rcu_dereference(vif->chanctx_conf);
+		struct ieee80211_chanctx_conf *chanctx_conf;
+
+		rcu_read_lock();
+		chanctx_conf = rcu_dereference(vif->chanctx_conf);
 
 		if (!WARN_ON(!chanctx_conf))
 			confbw = chanctx_conf->def.width;
+		rcu_read_unlock();
 	}
 
 	WARN(bw > hwsim_get_chanwidth(confbw),