Change string to "Maximum new connections per host / per second(s)"

Clarifying the setting's meaning.

As suggested by forum member "Senser" on
https://forum.pfsense.org/index.php/topic,65472.msg356024.html#msg356024
Merge pull request #913 from Aeyoun/string-max-connections-per-host-per-second

Change string to "Maximum new connections per host / per second(s)"