Add support for systemd service and watchdogs Fixes #2499.

[Matthew Newton]

On Wed, 2019-02-27 at 09:43 +0000, Stefano Mason wrote:
> "systemctl start radiusd.service" it doesn't exit but remain in a
> stuck state, it's necessary to do a CTRL-C, after that I check the
> status e the process list: all it's okay.

<sigh> thanks.

I've found the problem and working on a fix.

-- 
Matthew