add config entry in xml

Author: hfutatzhanghb

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/resources/hdfs-rbf-default.xml

@@ -152,6 +152,15 @@
     </description>
   </property>
 
+  <property>
+    <name>dfs.federation.router.async.rpc.max.asynccall.permit</name>
+    <value>20000</value>
+    <description>
+      Maximum number of asynchronous RPC requests the Router can send to
+      one downstream nameservice.
+    </description>
+  </property>
+
   <property>
     <name>dfs.federation.router.connection.creator.queue-size</name>
     <value>100</value>