Adds support for systemd's fd-passing socket activation, letting systemd
listen for connections before starting the service. This might enable
quicker startup on systems with dependent services, since they will now
only need to wait for the socket, which holds connections until kdc is
finished starting up. It also enables use of the `PrivateNetwork`
directive, sandboxing kadmind into it's own network namespace.
oysteikt
69e74be224
