Add log message if SSL dual mode is enabled (#16437)

* Add log message about dual mode enabled

Signed-off-by: Craig Perkins <cwperx@amazon.com>

* Add log message about dual mode enabled

Signed-off-by: Craig Perkins <cwperx@amazon.com>

---------

Signed-off-by: Craig Perkins <cwperx@amazon.com>

Author: cwperks

modules/transport-netty4/src/main/java/org/opensearch/transport/netty4/ssl/SecureNetty4Transport.java

@@ -146,6 +146,7 @@ protected void initChannel(Channel ch) throws Exception {
                 .map(SecureTransportSettingsProvider.SecureTransportParameters::dualModeEnabled)
                 .orElse(false);
             if (dualModeEnabled) {
+                logger.info("SSL Dual mode enabled, using port unification handler");
                 final ChannelHandler portUnificationHandler = new DualModeSslHandler(
                     settings,
                     secureTransportSettingsProvider,