test: modernized test to use arrow functions

PR-URL: #23496
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/parallel/test-dgram-send-callback-multi-buffer.js

@@ -6,19 +6,19 @@ const dgram = require('dgram');
 
 const client = dgram.createSocket('udp4');
 
-const messageSent = common.mustCall(function messageSent(err, bytes) {
+const messageSent = common.mustCall((err, bytes) => {
   assert.strictEqual(bytes, buf1.length + buf2.length);
 });
 
 const buf1 = Buffer.alloc(256, 'x');
 const buf2 = Buffer.alloc(256, 'y');
 
-client.on('listening', function() {
-  const port = this.address().port;
+client.on('listening', () => {
+  const port = client.address().port;
   client.send([buf1, buf2], port, common.localhostIPv4, messageSent);
 });
 
-client.on('message', common.mustCall(function onMessage(buf, info) {
+client.on('message', common.mustCall((buf, info) => {
   const expected = Buffer.concat([buf1, buf2]);
   assert.ok(buf.equals(expected), 'message was received correctly');
   client.close();