renamed Serializer -> (onlab.netty-layer) PayloadSerializer

- Added TODO memos to ClusterCommunicationService layer

Change-Id: I4c81a72d03cddd23637f9c6cbf102125ea448c01
diff --git a/utils/netty/src/main/java/org/onlab/netty/MessagingService.java b/utils/netty/src/main/java/org/onlab/netty/MessagingService.java
index ebad442..d455c94 100644
--- a/utils/netty/src/main/java/org/onlab/netty/MessagingService.java
+++ b/utils/netty/src/main/java/org/onlab/netty/MessagingService.java
@@ -38,4 +38,11 @@
      * @param type message type
      */
     public void unregisterHandler(String type);
+
+    /**
+     * Specify the serializer to use for encoding/decoding payload.
+     *
+     * @param payloadSerializer payloadSerializer to use
+     */
+    public void setPayloadSerializer(PayloadSerializer payloadSerializer);
 }