mt76: mt7915: disable RX_HDR_TRANS_SHORT

This patch disables RX_TRANS_SHORT to make MDP to do header translation
when payload less than 8 bytes, hence the (QoS) null data can be encapsulated
to 802.3 format. However, WDS requires (QoS) null data in 802.11 format
to created vlan AP interfaces.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: lian.chen <lian.chen@mediatek.com>
Signed-off-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Bo Jiao <Bo.Jiao@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>