add link handling in mt7925_txwi_free.

MT7996 should have the similar the logic, we try to copy from there to
ensure consistency between both.
Co-developed-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Signed-off-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Co-developed-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Link: https://patch.msgid.link/f8084e19d388c6b0807618ac6d1bb8ac633dc8cd.1720248331.git.sean.wang@kernel.orgSigned-off-by: Felix Fietkau <nbd@nbd.name>