cdc_ether: add usb id for Ericsson F3507g

The Ericsson F3507g wireless broadband module provides a CDC Ethernet
compliant interface, but identifies it as a "Mobile Direct Line" CDC
subclass, thereby preventing the CDC Ethernet class driver from picking
it up.  This patch adds the device id to cdc_ether.c as a workaround.

Ericsson has provided a "class" driver for this device:
http://kerneltrap.org/mailarchive/linux-net/2008/10/28/3832094
But closer inspection of that driver reveals that it adds little more
than duplication of code from cdc_ether.c.  See also
http://marc.info/?l=linux-usb&m=123334979706403&w=2

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