[sr-dev] [kamailio/kamailio] Systemd unit update (#1889)

[Juha Heinanen]

sergey-safarov writes:

> Now unit contains
> ```
> RuntimeDirectory=kamailio
> ```
...
> Look as current definition correct

Yes, RuntimeDirectory is correct, but not this:

PIDFile=/var/run/kamailio/kamailio.pid

since it hardwires /var/run rather than using $RUNTIME_DIRECTORY.

-- Juha