fix

Author: KeeProMise

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/async/RouterAsyncUserProtocol.java

@@ -25,7 +25,7 @@
 import static org.apache.hadoop.hdfs.server.federation.router.async.AsyncUtil.asyncComplete;
 import static org.apache.hadoop.hdfs.server.federation.router.async.AsyncUtil.asyncReturn;
 
-public class RouterAsyncUserProtocol implements RouterUserProtocol {
+public class RouterAsyncUserProtocol extends RouterUserProtocol {
   private static final Logger LOG =
       LoggerFactory.getLogger(RouterAsyncUserProtocol.class);