CaptivePortal check for getNasIP already exists

http://forum.pfsense.org/index.php/topic,66764.0.html
Do not committ this pull request - I think it should have a better solution that eliminates the code duplication of getNasIP in 2 places. A dev who knows how they want the include file hierarchy to work can sort that out. This pull request is just to highlight the issue reported in the forum.