net: cdc_ncm: tag Huawei devices (e.g. E5331) with FLAG_WWAN

Tag all Huawei NCM devices as WWAN modems, as we don't know of any which
are not.  This is necessary for userspace clients to know that the device
requires further setup on e.g. an AT-capable serial ports before
connectivity is available.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>