HDFS-15839. RBF: Cannot get method setBalancerBandwidth on Router Client. Contributed by Yang Yun.

Only Prod Changes: Test already cherry-picked as part of HDFS-16310 via (496657c63fc504dfeef47a3da56214800575367b)

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterClientProtocol.java

@@ -1179,7 +1179,7 @@ public class RouterClientProtocol implements ClientProtocol {
     rpcServer.checkOperation(NameNode.OperationCategory.UNCHECKED);
 
     RemoteMethod method = new RemoteMethod("setBalancerBandwidth",
-        new Class<?>[] {Long.class}, bandwidth);
+        new Class<?>[] {long.class}, bandwidth);
     final Set<FederationNamespaceInfo> nss = namenodeResolver.getNamespaces();
     rpcClient.invokeConcurrent(nss, method, true, false);
   }