code: public IPv6AddressRange extend(IPv6Address address)
      {
          if (address.compareTo(first) < 0)
              return fromFirstAndLast(address, last);
          else if (address.compareTo(last) > 0)
              return fromFirstAndLast(first, address);
          else
              return this;
      }
docs: Extend the range just enough at its head or tail such that the given address is included.
  
  @param address address to extend the range to
  @return new (bigger) range