comgt: ncm: select first available network interface for device

comgt: ncm: select first available network interface for device

Some modems expose multiple network interfaces on the same USB device,
causing the connection setup script to fail, because glob matching in
the detection phase causes 'ls' to output more than one interface name
plus their base directories in sysfs. Avoid that by listing the
directories explicitly and then selecting first available interface.
This is the case for some variants of ZTE MF286R built-in modem, which
exposes both RNDIS and CDC-ECM network interfaces, causing the
connection setup to fail.

Signed-off-by: Lech Perczak <lech.perczak@gmail.com>