Add ability to specify port range used by router mode workers

[ipilcher]

I am in the process of writing an SELinux policy for llama-server (currently focused on router mode). Under SELinux, TCP ports are labeled with specific types. (For example, TCP ports 80, 81, 443, 488, 8008, 8009, 8443, and 9000 are labeled as http_port_t on my Fedora 44 system.) Services are then allowed to bind/connect only to specific port types. (Apache httpd is allowed to bind only to TCP ports that are labeled as http_port_t.)

I ran into an obstacle when trying to apply this model to llama-server's router mode. llama.cpp currently provides no way to specify the range of ports that model workers will use, so it is impossible to label any particular set of ports with the correct label, such as a hypothetical llama_port_t.

My proposal is to add the ability to specify the port range used by workers, via both the command line and config.ini, probably something like --worker-port-min and --worker-port-max.

Any reason that a PR to implement this wouldn't be welcome?