usb: cdc_acm: Set bInterfaceProtocol to No Protocol (0)

Do not set protocol in interface descriptor. Although this field has
been ignored by major OSs during the last decades, this creates a big
deal of problems with ModemManager sending unexpected AT commands when
plugging in a dev board.

Fixes: #6646

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>