Merge pull request #2640 from areyouok/fix_resetOffset

[ISSUE #2449]  fix: resetOffset simultaneously will cause each message consume more than once

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

@@ -1105,7 +1105,7 @@ public class MQClientInstance {
         return null;
     }
 
-    public void resetOffset(String topic, String group, Map<MessageQueue, Long> offsetTable) {
+    public synchronized void resetOffset(String topic, String group, Map<MessageQueue, Long> offsetTable) {
         DefaultMQPushConsumerImpl consumer = null;
         try {
             MQConsumerInner impl = this.consumerTable.get(group);