SAP configuration applicable to internal SAP's associated
with a specific group interface.
Unlike regular subscriber traffic, that enters the system through
Service Access Points (SAP) on a group-interface,
some user traffic enters the system through a plain layer 3 interface;
this traffic is relayed for processing to an ISA MDA;
it re-enters through an internal SAP on an internal group interface;
this entry allows to configure certain SAP parameters for
those internal SAP's.
Current examples of such traffic are
- traffic for PPP subscriber sessions terminated by the LNS function,
- Wifi offload traffic, entering the system through a Soft-GRE tunnel.