INT-3800: Expose Actual Port Chosen When Random

JIRA: https://jira.spring.io/browse/INT-3800

If the server port is 0, return the actual port after the factory is started.

Also add more TCP Test Diagnostics.

src/reference/asciidoc/ip.adoc

@@ -166,6 +166,11 @@ A simple server connection factory that uses `java.net.Socket` connections.
 
 A simple server connection factory that uses `java.nio.channel.SocketChannel` connections.
 
+NOTE: Starting with Spring Integration _version 4.2_, if the server is configured to listen on a random port (0),
+the actual port chosen by the OS can be obtained using `getPort()`.
+Also, `getServerSocketAddress()` is available to get the complete `SocketAddress`.
+See the javadocs for the `TcpServerConnectionFactory` interface for more information.
+
 [source,xml]
 ----
 <int-ip:tcp-connection-factory id="client"

src/reference/asciidoc/whats-new.adoc

@@ -145,6 +145,15 @@ If you are using the serializers directly within user code, you may have to `flu
 `TcpConnectionServerExceptionEvent` s are now published whenever an unexpected exception occurs on a TCP server socket (also added to 4.1.3, 4.0.7).
 See <<tcp-events>> for more information.
 
+[[x4.2-tcp-server-port]]
+===== TCP Server Port
+
+If a TCP server socket factory is configured to listen on a random port, the actual port chosen by the OS can now
+be obtained using `getPort()`.
+`getServerSocketAddress()` is also available.
+
+See <<connection-factories>> for more information.
+
 [[x4.2-tcp-gw-rto]]
 ===== TCP Gateway Remote Timeout