/etc/freeradius/3.0/sites-enabled/default is in freeradius-config 3.0.12+dfsg-5+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /etc/freeradius/3.0/sites-enabled/../sites-available/default
/etc/freeradius/3.0/sites-enabled/../sites-available/default