if ipv6 is a range with prefix length N < 112:
  => give a unique ipv6 to each partition and a unique /N+16 range
if ipv6 is a range with prefix length >= 112
  => give a unique ipv6 to each partition
if ipv6 is not a range:
  => give the same ipv6 to each partition
Co-authored-by: Xavier Thompson <xavier.thompson@nexedi.com>