Bluetooth: btusb: Enable MSFT extension for WCN6855 controller

The Qualcomm WCN6855 Bluetooth controller supports the Microsoft vendor
extension, enable them by setting VsMsftOpCode to 0xFD70.

Verified on a WCN6855 device through bluetoothctl show

Signed-off-by: Michael Sun <michaelfsun@google.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>