HADOOP-17309. Javadoc warnings and errors are ignored in the precommit jobs. (#2391)

hadoop-project/pom.xml

@@ -1888,6 +1888,7 @@
           <artifactId>maven-javadoc-plugin</artifactId>
           <version>${maven-javadoc-plugin.version}</version>
           <configuration>
+            <doclint>all</doclint>
             <additionalOptions>
                 <additionalOption>-Xmaxwarns 10000</additionalOption>
             </additionalOptions>