wifi: mt76: mt7996: fix header translation logic

When header translation failure is indicated, the hardware will insert
an extra 2-byte field containing the data length after the protocol
type field. This happens either when the LLC-SNAP pattern did not match,
or if a VLAN header was detected.

The previous commit accidentally breaks the logic, so reverts back.

Fixes: 27db47ab (wifi: mt76: mt7996: enable mesh HW amsdu/de-amsdu support)
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7996/mac.c

@@ -836,14 +836,19 @@ mt7996_mac_fill_rx(struct mt7996_dev *dev, struct sk_buff *skb)
 		skb_pull(skb, hdr_gap);
 		if (!hdr_trans && status->amsdu && !(ieee80211_has_a4(fc) && is_mesh)) {
 			pad_start = ieee80211_get_hdrlen_from_skb(skb);
-		} else if (hdr_trans && (rxd2 & MT_RXD2_NORMAL_HDR_TRANS_ERROR) &&
-			   get_unaligned_be16(skb->data + pad_start) == ETH_P_8021Q) {
+		} else if (hdr_trans && (rxd2 & MT_RXD2_NORMAL_HDR_TRANS_ERROR)) {
 			/* When header translation failure is indicated,
 			 * the hardware will insert an extra 2-byte field
 			 * containing the data length after the protocol
-			 * type field.
+			 * type field. This happens either when the LLC-SNAP
+			 * pattern did not match, or if a VLAN header was
+			 * detected.
 			 */
-			pad_start = 16;
+			pad_start = 12;
+			if (get_unaligned_be16(skb->data + pad_start) == ETH_P_8021Q)
+				pad_start += 4;
+			else
+				pad_start = 0;
 		}
 
 		if (pad_start) {