wifi: mt76: drop the incorrect scatter and gather frame

The scatter and gather frame may be incorrect because WED and WO may
send frames to host driver interleaved.

Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Signed-off-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>