Implement get_v6_ptr_zones()
Implement get_v6_ptr_zones()

This function takes an IPv6 subnet and return an array containing all
DNS PTR zones

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