/usr/include/libmm-glib/ is in libmm-glib-dev 1.6.8-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/libmm-glib/libmm-glib.h
/usr/include/libmm-glib/mm-bearer-ip-config.h
/usr/include/libmm-glib/mm-bearer-properties.h
/usr/include/libmm-glib/mm-bearer-stats.h
/usr/include/libmm-glib/mm-bearer.h
/usr/include/libmm-glib/mm-call-properties.h
/usr/include/libmm-glib/mm-call.h
/usr/include/libmm-glib/mm-cdma-manual-activation-properties.h
/usr/include/libmm-glib/mm-enums-types.h
/usr/include/libmm-glib/mm-errors-types.h
/usr/include/libmm-glib/mm-firmware-properties.h
/usr/include/libmm-glib/mm-gdbus-bearer.h
/usr/include/libmm-glib/mm-gdbus-call.h
/usr/include/libmm-glib/mm-gdbus-manager.h
/usr/include/libmm-glib/mm-gdbus-modem.h
/usr/include/libmm-glib/mm-gdbus-sim.h
/usr/include/libmm-glib/mm-gdbus-sms.h
/usr/include/libmm-glib/mm-helper-types.h
/usr/include/libmm-glib/mm-location-3gpp.h
/usr/include/libmm-glib/mm-location-cdma-bs.h
/usr/include/libmm-glib/mm-location-common.h
/usr/include/libmm-glib/mm-location-gps-nmea.h
/usr/include/libmm-glib/mm-location-gps-raw.h
/usr/include/libmm-glib/mm-manager.h
/usr/include/libmm-glib/mm-modem-3gpp-ussd.h
/usr/include/libmm-glib/mm-modem-3gpp.h
/usr/include/libmm-glib/mm-modem-cdma.h
/usr/include/libmm-glib/mm-modem-firmware.h
/usr/include/libmm-glib/mm-modem-location.h
/usr/include/libmm-glib/mm-modem-messaging.h
/usr/include/libmm-glib/mm-modem-oma.h
/usr/include/libmm-glib/mm-modem-signal.h
/usr/include/libmm-glib/mm-modem-simple.h
/usr/include/libmm-glib/mm-modem-time.h
/usr/include/libmm-glib/mm-modem-voice.h
/usr/include/libmm-glib/mm-modem.h
/usr/include/libmm-glib/mm-network-timezone.h
/usr/include/libmm-glib/mm-object.h
/usr/include/libmm-glib/mm-signal.h
/usr/include/libmm-glib/mm-sim.h
/usr/include/libmm-glib/mm-simple-connect-properties.h
/usr/include/libmm-glib/mm-simple-status.h
/usr/include/libmm-glib/mm-sms-properties.h
/usr/include/libmm-glib/mm-sms.h
/usr/include/libmm-glib/mm-unlock-retries.h