The value of the object vRtrIfDHCP6LinkAddress specifies
the ipv6 address that will be used by the DHCP6 relay agent as
link address in all messages sent to the DHCP6 servers.
If set to ::, the system determines the link address
based on the group interface configuration.
This object can only be set when vRtrIfType is either
'serviceIesGroup(7)' or 'serviceVprnGroup(9)'.