test: fix flaky test-net-socket-local-address

test-net-socket-local-address had a race condition that resulted in
unreliability on FreeBSD and Windows. This changes fixes the issue.

Fixes: #2475

Author: Trott

test/parallel/parallel.status

@@ -21,4 +21,3 @@ test-child-process-exit-code         : PASS,FLAKY
 [$system==solaris] # Also applies to SmartOS
 
 [$system==freebsd]
-test-net-socket-local-address     : PASS,FLAKY

test/parallel/test-net-socket-local-address.js

@@ -15,7 +15,7 @@ var serverRemotePorts = [];
 
 const server = net.createServer(function(socket) {
   serverRemotePorts.push(socket.remotePort);
-  conns++;
+  testConnect();
 });
 
 const client = new net.Socket();
@@ -29,12 +29,17 @@ server.on('close', common.mustCall(function() {
 server.listen(common.PORT, common.localhostIPv4, testConnect);
 
 function testConnect() {
-  if (conns == 2) {
+  if (conns === 2) {
     return server.close();
   }
-  client.connect(common.PORT, common.localhostIPv4, function() {
-    clientLocalPorts.push(this.localPort);
-    this.once('close', testConnect);
-    this.destroy();
-  });
+  // conns === clientLocalPorts.length means both server and client callbacks
+  // have fired
+  if (conns === clientLocalPorts.length) {
+    client.connect(common.PORT, common.localhostIPv4, function() {
+      clientLocalPorts.push(this.localPort);
+      this.once('close', testConnect);
+      this.destroy();
+    });
+  }
+  conns++;
 }