umodem: add quirk to ignore CDC_CM descriptor

Some devices have CDC_CM descriptors that would point us to
the wrong interfaces. Add a quirk to ignore those (prefering the
CDC_UNION descriptor effectively)

Reviewed by: manu
MFC after: 1 week
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D37942