wifi: mt76: mt7925: keep TX BA state in the primary WCID

wifi: mt76: mt7925: keep TX BA state in the primary WCID

For MLO, the same TID can run over different links. Keeping TX BA state in
a link WCID makes the state depend on which link starts aggregation first.

Store it in the primary WCID instead, so the BA state stays stable across
links.

Fixes: 44eb173bdd4f ("wifi: mt76: mt7925: add link handling in mt7925_txwi_free")
Tested-by: Yao Ting Hsieh <yao-ting.hsieh@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/20260425154721.738101-1-sean.wang@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>