Pulledpork has a daily job to download rules. In this job suricata is reloaded to apply a new config but if suricata is not running you get Job for suricata.service invalid.
At the end of /etc/e-smith/events/actions/nethserver-pulledpork-apply suricata is reloaded.
This is called from /etc/cron.daily/pulledpork.
Cron then just mails the output. I think you can ignore it.
If you really don’t like it you may edit the systemctl reload suricata line at the end of /etc/e-smith/events/actions/nethserver-pulledpork-apply to
systemctl is-active --quiet suricata && systemctl reload suricata
but an update of pulledpork may overwrite it.