Expose the socket's local port in IMAPProtocol/Protocol - fix #356

doc/release/CHANGES.txt

@@ -25,6 +25,7 @@ longer available.
 The following bugs have been fixed in the 1.6.4 release.
 
 E  350	ServiceLoader loads default providers ahead of application providers
+E  356	Expose the socket's local port in IMAPProtocol/Protocol
 E  361	Support the NTLMv2 authentication protocol
 E  363	Multipart message sent with headers but no body
 E  366	NPE when recipients not set

mail/src/main/java/com/sun/mail/iap/Protocol.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2018 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2019 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0, which is available at
@@ -553,6 +553,17 @@ public SocketChannel getChannel() {
 	return ret;
     }
 
+    /**
+     * Return the local SocketAddress (host and port) for this
+     * end of the connection.
+     *
+     * @return	the SocketAddress
+     * @since	JavaMail 1.6.4
+     */
+    public SocketAddress getLocalSocketAddress() {
+	return socket.getLocalSocketAddress();
+    }
+
     /**
      * Does the server support UTF-8?
      * This implementation returns false.