[ROCKETMQ-153][HOTFIX] Fetch name server address dynamically.

client/src/main/java/org/apache/rocketmq/client/impl/factory/MQClientInstance.java

@@ -223,7 +223,7 @@ public class MQClientInstance {
                     this.serviceState = ServiceState.START_FAILED;
                     // If not specified,looking address from name server
                     if (null == this.clientConfig.getNamesrvAddr()) {
-                        this.clientConfig.setNamesrvAddr(this.mQClientAPIImpl.fetchNameServerAddr());
+                        this.mQClientAPIImpl.fetchNameServerAddr();
                     }
                     // Start request-response channel
                     this.mQClientAPIImpl.start();