Bluetooth: btmtkuart: fix the conflict between mtk and msft vendor event

There is a conflict between MediaTek wmt event and msft vendor extension
logic in the core layer since 145373cb1b1f ("Bluetooth: Add framework for
Microsoft vendor extension") was introduced because we changed the type of
mediatek wmt event to the type of msft vendor event in the driver.

But the purpose we reported mediatek event to the core layer is for the
diagnostic purpose with that we are able to see the full packet trace via
monitoring socket with btmon. Thus, it is harmless we keep the original
type of mediatek vendor event here to avoid breaking the msft extension
function especially they can be supported by Mediatek future devices.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>