netty4 OpenFlow southbound

- separate I/O thread and message dispatch threads

Change-Id: I11a10a47de451a9e3063b62f9450be19c3a9dae7
diff --git a/providers/null/pom.xml b/providers/null/pom.xml
index 321de42..7490d37 100644
--- a/providers/null/pom.xml
+++ b/providers/null/pom.xml
@@ -55,6 +55,11 @@
         </dependency>
 
         <dependency>
+            <groupId>io.netty</groupId>
+            <artifactId>netty</artifactId>
+        </dependency>
+
+        <dependency>
             <groupId>org.onosproject</groupId>
             <artifactId>onos-api</artifactId>
             <classifier>tests</classifier>