test: don't assume broadcast traffic is unfiltered

parallel/test-dgram-broadcast-multi-process assumes non-local broadcast
traffic is unfiltered, an assumption that fails with, for example, the
default Fedora firewall rules.  Use a loopback interface instead.

Fixes: #219
PR-URL: #220
Reviewed-By: Fedor Indutny <fedor@indutny.com>

test/parallel/test-dgram-broadcast-multi-process.js

@@ -23,7 +23,6 @@ var common = require('../common'),
     assert = require('assert'),
     dgram = require('dgram'),
     util = require('util'),
-    networkInterfaces = require('os').networkInterfaces(),
     Buffer = require('buffer').Buffer,
     fork = require('child_process').fork,
     LOCAL_BROADCAST_HOST = '255.255.255.255',
@@ -35,19 +34,6 @@ var common = require('../common'),
       new Buffer('Fourth message to send')
     ];
 
-// take the first non-internal interface as the address for binding
-get_bindAddress: for (var name in networkInterfaces) {
-  var interfaces = networkInterfaces[name];
-  for(var i = 0; i < interfaces.length; i++) {
-    var localInterface = interfaces[i];
-    if (!localInterface.internal && localInterface.family === 'IPv4') {
-      var bindAddress = localInterface.address;
-      break get_bindAddress;
-    }
-  }
-}
-assert.ok(bindAddress);
-
 if (process.argv[2] !== 'child') {
   var workers = {},
       listeners = 3,
@@ -164,7 +150,7 @@ if (process.argv[2] !== 'child') {
 
   // bind the address explicitly for sending
   // INADDR_BROADCAST to only one interface
-  sendSocket.bind(common.PORT, bindAddress);
+  sendSocket.bind(common.PORT, '127.0.0.1');
   sendSocket.on('listening', function () {
     sendSocket.setBroadcast(true);
   });
@@ -211,7 +197,7 @@ if (process.argv[2] === 'child') {
 
   listenSocket.on('message', function(buf, rinfo) {
     // receive udp messages only sent from parent
-    if (rinfo.address !== bindAddress) return;
+    if (rinfo.address !== '127.0.0.1') return;
 
     console.error('[CHILD] %s received %s from %j',
                   process.pid,