HADOOP-15849. Upgrade netty version to 3.10.6.

hadoop-project/pom.xml

@@ -961,7 +961,7 @@
       <dependency>
         <groupId>io.netty</groupId>
         <artifactId>netty</artifactId>
-        <version>3.10.5.Final</version>
+        <version>3.10.6.Final</version>
       </dependency>
 
       <dependency>