Enables the PortBundle-Host Key feature, which lets the companion SESM system identify an individual subscriber by the combination of a shared IP address plus a specific range of ports assigned to that subscriber by SSG. This is specifically the mechanism that makes per-subscriber service selection work when many subscribers are hidden behind one NATed IP, because without a distinguishing port range SESM would only see one IP and couldn't tell which of many subscribers a packet belongs to. A carrier running large-scale NAT for mobile broadband, with thousands of subscribers sharing a handful of public IPs, would enable cssgCfgPortBundleHostKeyEnabled and configure cssgPortMapLength/PortRangeFrom/PortRangeTo so each subscriber gets, say, ports 20000-20099 to stay individually identifiable.