wifi: mt76: Fix possible oob access in mt76_connac2_mac_write_txwi_80211()

wifi: mt76: Fix possible oob access in mt76_connac2_mac_write_txwi_80211()

Check frame length before accessing the mgmt fields in
mt76_connac2_mac_write_txwi_80211 in order to avoid a possible oob
access.

Fixes: 577dbc6c656d ("mt76: mt7915: enable offloading of sequence number assignment")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260226-mt76-addba-req-oob-access-v1-3-b0f6d1ad4850@kernel.org
[fix check to also cover mgmt->u.action.u.addba_req.capab,
correct Fixes tag]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>