INT-3894: Polishing

Remove IPv4 from build.gradle.
Fix race for ackPort.

build.gradle

@@ -401,10 +401,6 @@ project('spring-integration-ip') {
 		compile project(":spring-integration-core")
 		testCompile project(":spring-integration-stream")
 	}
-
-	test {
-		jvmArgs '-Djava.net.preferIPv4Stack=true' // Multicast on OS X
-	}
 }
 
 project('spring-integration-jdbc') {

spring-integration-ip/src/main/java/org/springframework/integration/ip/udp/UnicastSendingMessageHandler.java

@@ -256,6 +256,12 @@ public class UnicastSendingMessageHandler extends
 		if (!this.ackThreadRunning) {
 			synchronized(this) {
 				if (!this.ackThreadRunning) {
+					try {
+						getSocket();
+					}
+					catch (IOException e) {
+						logger.error("Error creating socket", e);
+					}
 					ackLatch = new CountDownLatch(1);
 					this.taskExecutor.execute(this);
 					try {