--------------------------------------------------------------------------------
I've played around with this and found out a few things:

The @controller_issues_new_before_save@ hook seems like the best fit if this were to be a plugin however the methods used to get the IP Address and Device Name in Ruby are not available in a @Redmine::Hook::ViewListener@ class. These methods are only available in a controller.

That being said, custom field values can still be set here. If the methods could somehow become available in the @Redmine::Hook::ViewListener@ class then this issue would be resolved. As it stands, one would have to get the IP Address and Device Name in their plugin controller, store these values in variables, and then somehow re-direct to the regular issue creation which calls the hook that actually sets the fields.

I don't claim to be an expert in Redmine, Rails, or Ruby. So if someone sees a better solution don't hesitate to comment.
--------------------------------------------------------------------------------