Replace the config path with the flag

The sample in the porters hadbook has a daemon with a config file,
lldpd doesn't have a config file thus we provide a config flag.

Thanks for the pointer towards postfix and later varnish via IRC.
Unbreak execution

That's why you have to test in a clean environment,
not only did we influence the privsep chroot, but also we
have to point to another runstatedir (or create it, which would
be /usr/local/var/run.)