comgt: ncm: try to detect interface for ttyACM ports

comgt: ncm: try to detect interface for ttyACM ports

Some modems expose ttyACM as their control ports, which have the
"device" symlink pointing one level down in sysfs tree. Try to find
network interfaces for them as well, this is commonly used for modems
exposing ACM + RNDIS or ACM + ECM interface combinations.

Co-developed-by: Cezary Jackiewicz <cezary@eko.one.pl>
Signed-off-by: Cezary Jackiewicz <cezary@eko.one.pl>
Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
(cherry picked from commit ed7957810c0aee04943559be9b0ed23431ee0654)