To be able to label incoming tor connections as different from normal localhost connections in e.g. `getpeerinfo` and the peers list in the GUI it'd be useful to have them connect on an alternative local-only port. Or even better, a UNIX socket.

For manually set-up hidden services this would have to be configured manually and could add a `hsport` option or such. The external port would still appear as `XXXXXXXXX.onion:8333`, however internally it would redirect to a that port.

In the case of `torcontrol` this would be easy to set up automatically. It could add a new (localhost) binding port automatically and this code would have to be changed:
- https://github.com/bitcoin/bitcoin/blob/master/src/torcontrol.cpp#L441
- https://github.com/bitcoin/bitcoin/blob/master/src/torcontrol.cpp#L477

{
    if (!g_upnp_thread.joinable()) {
        assert(!g_upnp_interrupt);
        g_upnp_thread = std::thread((std::bind(&TraceThread<void (*)()>, "upnp", &ThreadMapPort)));
    }
}
void InterruptMapPort()
{
    if(g_upnp_thread.joinable()) {
        g_upnp_interrupt();
    }
}
void StopMapPort()
{
    if(g_upnp_thread.joinable()) {
        g_upnp_thread.join();
        g_upnp_interrupt.reset();
    }
}
#else
void StartMapPort()