/usr/src/linux-headers-4.15.0-39-generic/net is in linux-headers-4.15.0-39-generic 4.15.0-39.42.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/src/linux-headers-4.15.0-39-generic/../linux-headers-4.15.0-39/net