cdc_ether: flag the u-blox TOBY-L2 and SARA-U2 as wwan

The u-blox TOBY-L2 is a LTE Cat 4 module with HSPA+ and 2G fallback.
This module allows switching to different USB profiles with the
'AT+UUSBCONF' command, and provides a ECM network interface when the
'AT+UUSBCONF=2' profile is selected.

The u-blox SARA-U2 is a HSPA module with 2G fallback. The default USB
configuration includes a ECM network interface.

Both these modules are controlled via AT commands through one of the
TTYs exposed. Connecting these modules may be done just by activating
the desired PDP context with 'AT+CGACT=1,<cid>' and then running DHCP
on the ECM interface.

Signed-off-by: Aleksander Morgado <aleksander@aleksander.es>
Signed-off-by: David S. Miller <davem@davemloft.net>