Added support for IPv6 addresses to class IpAddress:

 - For some of the methods, the IP Version needs to be specified by the
   caller. This applies to the IpPrefix API as well.
 - For now, everywhere IpAddress is used and the IP version has to be
   explicitly specified by the caller, we assume/specify IPv4.
 - Added unit test for class IpAddress: for both IPv4 and IPv6 addresses.
diff --git a/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/IpPrefixSerializer.java b/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/IpPrefixSerializer.java
index 004f75f..5d895d7 100644
--- a/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/IpPrefixSerializer.java
+++ b/core/store/serializers/src/main/java/org/onlab/onos/store/serializers/IpPrefixSerializer.java
@@ -15,6 +15,7 @@
  */
 package org.onlab.onos.store.serializers;
 
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.IpPrefix;
 
 import com.esotericsoftware.kryo.Kryo;
@@ -51,6 +52,7 @@
         byte[] octs = new byte[octLen];
         input.readBytes(octs);
         int prefLen = input.readInt();
-        return IpPrefix.valueOf(octs, prefLen);
+        // TODO: Add support for reading/writing the IP version
+        return IpPrefix.valueOf(IpAddress.Version.INET, octs, prefLen);
     }
 }