mt76: mt76x02: only override control->sta on sw-encrypted tx

control->sta is set to NULL early when encryption is turned on for the
station and info->control.hw_key is not set.
This code is missing a check for the 802.11 header protected flag, otherwise
it resets the station for other frames, e.g. client probing frames.
Signed-off-by: NFelix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76x02_txrx.c

@@ -22,6 +22,7 @@
 void mt76x02_tx(struct ieee80211_hw *hw, struct ieee80211_tx_control *control,
 		struct sk_buff *skb)
 {
+	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 	struct mt76x02_dev *dev = hw->priv;
 	struct ieee80211_vif *vif = info->control.vif;
@@ -33,7 +34,8 @@ void mt76x02_tx(struct ieee80211_hw *hw, struct ieee80211_tx_control *control,
 		msta = (struct mt76x02_sta *)control->sta->drv_priv;
 		wcid = &msta->wcid;
 		/* sw encrypted frames */
-		if (!info->control.hw_key && wcid->hw_key_idx != 0xff)
+		if (!info->control.hw_key && wcid->hw_key_idx != 0xff &&
+		    ieee80211_has_protected(hdr->frame_control))
 			control->sta = NULL;
 	}