fix for #2356 'track interface'
fix for #2356 'track interface'

convert pulldown for ipv6 prefix id to a textbox.  validation is
implemented.

BlackstarGroup/pfsense,ch1c4um/pfsense,brunostein/pfsense,NewEraCracker/pfsense,BlackstarGroup/pfsense,phil-davis/pfsense,phil-davis/pfsense,pfsense/pfsense,ptorsten/pfsense,phil-davis/pfsense,brunostein/pfsense,jxmx/pfsense,jxmx/pfsense,NOYB/pfsense,jxmx/pfsense,BlackstarGroup/pfsense,dennypage/pfsense,NewEraCracker/pfsense,ptorsten/pfsense,BlackstarGroup/pfsense,pfsense/pfsense,brunostein/pfsense,NOYB/pfsense,ptorsten/pfsense,pfsense/pfsense,ch1c4um/pfsense,dennypage/pfsense,dennypage/pfsense,NewEraCracker/pfsense,NewEraCracker/pfsense,pfsense/pfsense,phil-davis/pfsense,ch1c4um/pfsense,ch1c4um/pfsense,dennypage/pfsense,NOYB/pfsense