/usr/include/NetworkManager/ is in libnm-util-dev 1.6.2-3+deb9u2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/NetworkManager/nm-connection.h
/usr/include/NetworkManager/nm-setting-8021x.h
/usr/include/NetworkManager/nm-setting-adsl.h
/usr/include/NetworkManager/nm-setting-bluetooth.h
/usr/include/NetworkManager/nm-setting-bond.h
/usr/include/NetworkManager/nm-setting-bridge-port.h
/usr/include/NetworkManager/nm-setting-bridge.h
/usr/include/NetworkManager/nm-setting-cdma.h
/usr/include/NetworkManager/nm-setting-connection.h
/usr/include/NetworkManager/nm-setting-dcb.h
/usr/include/NetworkManager/nm-setting-generic.h
/usr/include/NetworkManager/nm-setting-gsm.h
/usr/include/NetworkManager/nm-setting-infiniband.h
/usr/include/NetworkManager/nm-setting-ip4-config.h
/usr/include/NetworkManager/nm-setting-ip6-config.h
/usr/include/NetworkManager/nm-setting-olpc-mesh.h
/usr/include/NetworkManager/nm-setting-ppp.h
/usr/include/NetworkManager/nm-setting-pppoe.h
/usr/include/NetworkManager/nm-setting-serial.h
/usr/include/NetworkManager/nm-setting-team-port.h
/usr/include/NetworkManager/nm-setting-team.h
/usr/include/NetworkManager/nm-setting-vlan.h
/usr/include/NetworkManager/nm-setting-vpn.h
/usr/include/NetworkManager/nm-setting-wimax.h
/usr/include/NetworkManager/nm-setting-wired.h
/usr/include/NetworkManager/nm-setting-wireless-security.h
/usr/include/NetworkManager/nm-setting-wireless.h
/usr/include/NetworkManager/nm-setting.h
/usr/include/NetworkManager/nm-utils-enum-types.h
/usr/include/NetworkManager/nm-utils.h