HDFS-15508. [JDK 11] Fix javadoc errors in hadoop-hdfs-rbf module

hadoop-hdfs-project/hadoop-hdfs-rbf/pom.xml

@@ -31,7 +31,6 @@ https://maven.apache.org/xsd/maven-4.0.0.xsd">
 
   <properties>
     <hadoop.component>hdfs</hadoop.component>
-    <javadoc.skip.jdk11>true</javadoc.skip.jdk11>
   </properties>
 
   <dependencies>

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/security/token/package-info.java

@@ -18,7 +18,8 @@
 
 /**
  * Includes implementations of token secret managers.
- * Implementations should extend {@link AbstractDelegationTokenSecretManager}.
+ * Implementations should extend
+ * {@link org.apache.hadoop.security.token.delegation.AbstractDelegationTokenSecretManager}.
  */
 @InterfaceAudience.Private
 @InterfaceStability.Evolving