usbnet: add support for some Huawei modems with cdc-ether ports

Some newer Huawei devices (T-Mobile Rocket, others) have cdc-ether
compatible ports, so recognize and expose them.

Signed-off-by: Dan Williams <dcbw@redhat.com>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>