HDFS-13195. DataNode conf page cannot display the current value after reconfig. Contributed by maobaolong.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/web/DatanodeHttpServer.java

@@ -120,6 +120,7 @@ public class DatanodeHttpServer implements Closeable {
 
     this.infoServer = builder.build();
 
+    this.infoServer.setAttribute(HttpServer2.CONF_CONTEXT_ATTRIBUTE, conf);
     this.infoServer.setAttribute("datanode", datanode);
     this.infoServer.setAttribute(JspHelper.CURRENT_CONF, conf);
     this.infoServer.addServlet(null, "/blockScannerReport",