collectd: Restart is required after reconnect

collectd: Restart is required after reconnect

The "ping" plugin does not re-resolve the gateway IP address after
pinging it for the first time. For most people this won't be a big
problem, but if the default gateway changes, the latency graph won't
work any more.

In order to do re-resolve "gateway", the only way is to restart
collectd.

Fixes: #13522
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
Acked-by: Peter Müller <peter.mueller@ipfire.org>