Workaround for NoClassDefFound issue in Netty.

SimpleChannelInboundHandler generates `message` instance check code on the fly,
using JavaAssist. Which was not working, when a new Connection was created on the thread
outside of NettyMessagingManager bundle, which did not have access to netty classes.
- Implemented equivalent for SimpleChannelInboundHandler<InternaleMessage>
  without specifying type parameter, avoiding on the fly code generation.

Other changes:
- Add a method in IpAddress to return InetAddress instance.

Change-Id: Ie97294a5650683457b9395e773269c5232d8e602
diff --git a/utils/misc/src/main/java/org/onlab/packet/IpAddress.java b/utils/misc/src/main/java/org/onlab/packet/IpAddress.java
index f47b065..bf01406 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IpAddress.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IpAddress.java
@@ -16,6 +16,7 @@
 package org.onlab.packet;
 
 import java.net.InetAddress;
+import java.net.UnknownHostException;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
 import java.nio.ByteBuffer;
@@ -142,6 +143,20 @@
     }
 
     /**
+     * Returns the IP address as InetAddress.
+     *
+     * @return InetAddress
+     */
+    public InetAddress toInetAddress() {
+        try {
+            return InetAddress.getByAddress(octets);
+        } catch (UnknownHostException e) {
+            // Should never reach here
+            return null;
+        }
+    }
+
+    /**
      * Computes the IP address byte length for a given IP version.
      *
      * @param version the IP version