Finalise setup of internal IP variables

We IPv4 we look for for files named:
  MULTICAST_IPV4 but will use MULTICAST_IPS if it is all their is
  PRIVATE_IPV4 but will use PRIVATE_IPS if it is all their is
  RESERVED_IPV4 but will use RESERVED_IPS if it is all their is

For IPv6 we look for files named:
  MULTICAST_IPV6
  RESERVED_IPV6
  PRIVATE_IPV6

Within a configuration the variables can be used as:
  router src4 not "$PRIVATE_IPV4" src6 not "$PRIVATE_IPV6"

or using the equivalent 'special variable' which expands according to need:
  router src not "$PRIVATE_IPS"