/usr/include/libnm-glib/ is in libnm-glib-dev 1.2.6-0ubuntu0.16.04.3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/libnm-glib/libnm_glib.h
/usr/include/libnm-glib/nm-access-point.h
/usr/include/libnm-glib/nm-active-connection.h
/usr/include/libnm-glib/nm-client.h
/usr/include/libnm-glib/nm-device-adsl.h
/usr/include/libnm-glib/nm-device-bond.h
/usr/include/libnm-glib/nm-device-bridge.h
/usr/include/libnm-glib/nm-device-bt.h
/usr/include/libnm-glib/nm-device-ethernet.h
/usr/include/libnm-glib/nm-device-generic.h
/usr/include/libnm-glib/nm-device-infiniband.h
/usr/include/libnm-glib/nm-device-modem.h
/usr/include/libnm-glib/nm-device-olpc-mesh.h
/usr/include/libnm-glib/nm-device-team.h
/usr/include/libnm-glib/nm-device-vlan.h
/usr/include/libnm-glib/nm-device-wifi.h
/usr/include/libnm-glib/nm-device-wimax.h
/usr/include/libnm-glib/nm-device.h
/usr/include/libnm-glib/nm-dhcp4-config.h
/usr/include/libnm-glib/nm-dhcp6-config.h
/usr/include/libnm-glib/nm-glib-enum-types.h
/usr/include/libnm-glib/nm-ip4-config.h
/usr/include/libnm-glib/nm-ip6-config.h
/usr/include/libnm-glib/nm-object.h
/usr/include/libnm-glib/nm-remote-connection.h
/usr/include/libnm-glib/nm-remote-settings.h
/usr/include/libnm-glib/nm-secret-agent.h
/usr/include/libnm-glib/nm-types.h
/usr/include/libnm-glib/nm-vpn-connection.h
/usr/include/libnm-glib/nm-wimax-nsp.h