net: usb: cdc_ether: Use wwan interface for Telit modules

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: <stable@vger.kernel.org> # 3.0+ as far back as it applies cleanly
Acked-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: David S. Miller <davem@davemloft.net>