test: use the new net.listen(backlog=x) API

test/fixtures/fork2.js

@@ -16,10 +16,7 @@ process.on('message', function(m, serverHandle) {
     process.send({ childConnections: connections });
   });
 
-  // TODO need better API for this.
-  server._backlog = 9;
-
-  server.listen(serverHandle, function() {
+  server.listen(serverHandle, /* backlog */ 9, function() {
     process.send({ gotHandle: true });
   });
 });

test/simple/test-child-process-fork2.js

@@ -36,10 +36,7 @@ var server = new net.Server(function(c) {
   c.destroy();
 });
 
-// TODO need better API for this.
-server._backlog = 9;
-
-server.listen(common.PORT, function() {
+server.listen(common.PORT, /* backlog */ 9, function() {
   console.log('PARENT send child server handle');
   n.send({ hello: 'world' }, server._handle);
 });