net: qmi_wwan: add support for ZTE MF820D

ZTE have yet to discover the magic of USB descriptors.  These
devices use ff/ff/ff for class/subclass/protocol regardless of
function, except for usb-storage.  Use an interface number
whitelist to force the driver to bind only to the QMI/wwan
interface.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>