mt76: mt7915: use ieee80211_free_txskb to free tx skbs

Using dev_kfree_skb for tx skbs breaks AQL. This worked until now only
by accident, because a mac80211 issue breaks AQL on drivers with firmware
rate control that report the rate via ieee80211_tx_status_ext as struct
rate_info.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200812144943.91974-1-nbd@nbd.name

drivers/net/wireless/mediatek/mt76/mt7915/init.c

@@ -699,8 +699,12 @@ void mt7915_unregister_device(struct mt7915_dev *dev)
 	spin_lock_bh(&dev->token_lock);
 	idr_for_each_entry(&dev->token, txwi, id) {
 		mt7915_txp_skb_unmap(&dev->mt76, txwi);
-		if (txwi->skb)
-			dev_kfree_skb_any(txwi->skb);
+		if (txwi->skb) {
+			struct ieee80211_hw *hw;
+
+			hw = mt76_tx_status_get_hw(&dev->mt76, txwi->skb);
+			ieee80211_free_txskb(hw, txwi->skb);
+		}
 		mt76_put_txwi(&dev->mt76, txwi);
 	}
 	spin_unlock_bh(&dev->token_lock);

drivers/net/wireless/mediatek/mt76/mt7915/mac.c

@@ -841,7 +841,7 @@ mt7915_tx_complete_status(struct mt76_dev *mdev, struct sk_buff *skb,
 	if (sta || !(info->flags & IEEE80211_TX_CTL_NO_ACK))
 		mt7915_tx_status(sta, hw, info, NULL);
 
-	dev_kfree_skb(skb);
+	ieee80211_free_txskb(hw, skb);
 }
 
 void mt7915_txp_skb_unmap(struct mt76_dev *dev,