wifi: mt76: mt7996: fix pointer calculation in ie countdown event

Fix the tail and data pointers. The rxd->len in mt7996_mcu_rxd does not
include the length of general rxd. It only includes the length of
firmware event rxd. Use skb->length to get the correct length.

Fixes: 98686cd2 ("wifi: mt76: mt7996: add driver for MediaTek Wi-Fi 7 (802.11be) devices")
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

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

@@ -422,7 +422,8 @@ mt7996_mcu_ie_countdown(struct mt7996_dev *dev, struct sk_buff *skb)
 	if (hdr->band && dev->mt76.phys[hdr->band])
 		mphy = dev->mt76.phys[hdr->band];
 
-	tail = skb->data + le16_to_cpu(rxd->len);
+	tail = skb->data + skb->len;
+	data += sizeof(struct header);
 	while (data + sizeof(struct tlv) < tail && le16_to_cpu(tlv->len)) {
 		switch (le16_to_cpu(tlv->tag)) {
 		case UNI_EVENT_IE_COUNTDOWN_CSA: