fix javadoc

Author: KeeProMise

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

@@ -664,6 +664,8 @@ public Object invokeMethod(
    * "clientId:id", "clientCallId:callId" and "realUser:userName"
    * in the caller context, removing the old values if they were
    * already present.
+   *
+   * @param ugi User group information.
    */
   protected void addClientInfoToCallerContext(UserGroupInformation ugi) {
     CallerContext ctx = CallerContext.getCurrent();