Subscriber Services: Dual-stack, single-session authentication & reauthentication enhancements

Reauthentication is supported in response to DHCP discover and solicit messages, in addition to the previously supported renew and rebind messages. Reauthentication is supported for DHCP dual-stack, single-session subscribers when on-demand address allocation is configured. Both authentication and reauthentication for dual-stack, single-session supports are performed per family in the stack, using separate Access-Requests to the RADIUS server.