Fix the reverse look zone look up to handle non /24 CDIR

[cho00013]

Currently the code only handles if the PTR zone is 255.255.255.0. That should be fine for Census but I think to make the code more complete, it should also be able to handle /16.

[badra001]

In DNS, the zones for IPv4 are created only for /24 boundaries. You can get this from the ipaddress python module

import ipaddress

ip=ipaddress.ip_address(ip_address_string)
rev_ip=ip.reverse_pointer
v=ip.version

if v==4:
  np='.'.join(p.split('.')[1:])
elif v==6:
  np='.'.join(p.split('.')[16:])
else:
  np='undefined'

# np is the string for the PTR zone, either ipv4 format (/24) or ipv6 format (/64).

We do want to make sure we can extend this for IPv6 easily.