FIX: Require a selection for Zeek/Suricata cores

[dougburks]

Originally posted by @xfaith in https://github.com/Security-Onion-Solutions/securityonion/discussions/8402

Under the advance setup for the # of cores for Zeek/Suricata, if you dont "select" the number of cores, it lets you move on without a notification of no core selected. I only noticed this when I got the the review stage.

I had highlighted # of cores for suricata (did not select it though), and hit enter, which brought me to the next step in the install. I noticed when i checked the review that I had 0 core assigned to suricata.

Might be good to have some sort of error check here that makes sure the user selects any of the available numbers.