mt76: connac: fix HT A-MPDU setting field in STA_REC_PHY

The MT7921 firmware needs this to enable tx A-MPDU properly

Reported-by: Jayden Kuo (郭育辰) <Jayden.Kuo@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210507100211.15709-1-nbd@nbd.name