Modems with ECM (e.g. usb0) ports should use AT^NDISDUP in the control port to
request the connection and afterwards just fire up the DHCP client in the net
port.
This patch is originally developed by:
Franko Fang <fangxiaozhi@huawei.com>
And afterwareds reviewed and updated by:
Aleksander Morgado <aleksander@gnu.org>