mt76: connac: fix sta_rec_wtbl tag len

Similar to mt7915 driver, fix tag len error for sta_rec_wtbl, which
causes fw parsing error for the tags placed behind it.

Fixes: d0e274af ("mt76: mt76_connac: create mcu library")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c

@@ -310,7 +310,7 @@ mt76_connac_mcu_alloc_wtbl_req(struct mt76_dev *dev, struct mt76_wcid *wcid,
 	}
 
 	if (sta_hdr)
-		sta_hdr->len = cpu_to_le16(sizeof(hdr));
+		le16_add_cpu(&sta_hdr->len, sizeof(hdr));
 
 	return skb_put_data(nskb, &hdr, sizeof(hdr));
 }