Support for DHCPv6 NotOnLink status code

The DHCPv6 server can return to the client a status code of NotOnLink in the Reply PDU IA field during reauthentication when the subscriber IP or IPv6 address changes. This code means that at least one address in the client's request IA is not appropriate for the client's connection link. In earlier releases, only a NoAddrsAvail or NoPrefixAvail status code can be returned when there is an issue with requested addresses.