wifi: mt76: connac: update struct sta_rec_phy

For connac3 generation, max_ampdu_len should be filled in
struct sta_rec_phy.
This is a preliminary patch to add mt7996 chipset support.

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>