wifi: mt76: mt7921: add mt7921_mutex_acquire at mt7921_sta_set_decap_offload

Add mt7921_mutex_acquire at mt7921_[start, stop]_ap to fix the race
with the context holding dev->muxtex and the driver might access the
device in low power state.

Fixes: 24299fc8 ("mt76: mt7921: enable rx header traslation offload")
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7921/main.c

@@ -1404,6 +1404,8 @@ static void mt7921_sta_set_decap_offload(struct ieee80211_hw *hw,
 	struct mt7921_sta *msta = (struct mt7921_sta *)sta->drv_priv;
 	struct mt7921_dev *dev = mt7921_hw_dev(hw);
 
+	mt7921_mutex_acquire(dev);
+
 	if (enabled)
 		set_bit(MT_WCID_FLAG_HDR_TRANS, &msta->wcid.flags);
 	else
@@ -1411,6 +1413,8 @@ static void mt7921_sta_set_decap_offload(struct ieee80211_hw *hw,
 
 	mt76_connac_mcu_sta_update_hdr_trans(&dev->mt76, vif, &msta->wcid,
 					     MCU_UNI_CMD(STA_REC_UPDATE));
+
+	mt7921_mutex_release(dev);
 }
 
 #if IS_ENABLED(CONFIG_IPV6)