Add host/port "switchboard" module

Centrally list all hostnames and port numbers here. Need to push
this into IDZ further but I'm a bit short on time (so what else is
new).

src/idz/ping.ts

@@ -1,9 +1,9 @@
 import { createSocket } from "dgram";
 
-export default function createPing(port: number) {
+export default function createPing(port: number, host: string) {
   const socket = createSocket("udp4");
 
-  socket.bind(port);
+  socket.bind(port, host);
   socket.on("message", (msg, rinfo) => {
     console.log(`Idz Ping: Ping from ${rinfo.address}:${rinfo.port}`);
     socket.send(msg, rinfo.port, rinfo.address);