test: fix flaky test-net-can-reset-timeout

Use `.once()` rather than `.on()` for timeout listener.

Add comment with URL for issue explaining the purpose of the test. (h/t
refack)

PR-URL: nodejs#14257
Fixes: nodejs#14241
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>

test/parallel/test-net-can-reset-timeout.js

@@ -21,14 +21,17 @@
 
 'use strict';
 const common = require('../common');
+
+// Ref: https://github.com/nodejs/node-v0.x-archive/issues/481
+
 const net = require('net');
 
 const server = net.createServer(common.mustCall(function(stream) {
   stream.setTimeout(100);
 
   stream.resume();
 
-  stream.on('timeout', common.mustCall(function() {
+  stream.once('timeout', common.mustCall(function() {
     console.log('timeout');
     // try to reset the timeout.
     stream.write('WHAT.');