[ROCKETMQ-315] Enhance TLS default settings

Author: shutian.lzh <shutian.lzh@alibaba-inc.com>

Closes #194 from lizhanhui/tls_enhance_defaults.

broker/src/main/java/org/apache/rocketmq/broker/BrokerStartup.java

@@ -98,7 +98,7 @@ public class BrokerStartup {
             final BrokerConfig brokerConfig = new BrokerConfig();
             final NettyServerConfig nettyServerConfig = new NettyServerConfig();
             final NettyClientConfig nettyClientConfig = new NettyClientConfig();
-            nettyClientConfig.setUseTLS(NettySystemConfig.sslMode != SslMode.DISABLED);
+            nettyClientConfig.setUseTLS(NettySystemConfig.sslMode == SslMode.ENFORCING);
             nettyServerConfig.setListenPort(10911);
             final MessageStoreConfig messageStoreConfig = new MessageStoreConfig();
 

remoting/src/main/java/org/apache/rocketmq/remoting/netty/NettySystemConfig.java

@@ -57,7 +57,7 @@ public class NettySystemConfig {
      * </ol>
      */
     public static SslMode sslMode = //
-        SslMode.parse(System.getProperty(ORG_APACHE_ROCKETMQ_REMOTING_SSL_MODE, "disabled"));
+        SslMode.parse(System.getProperty(ORG_APACHE_ROCKETMQ_REMOTING_SSL_MODE, "permissive"));
 
     public static String sslConfigFile = //
         System.getProperty(ORG_APACHE_ROCKETMQ_REMOTING_SSL_CONFIG_FILE, "/etc/rocketmq/ssl.properties");