Various fixes

Change-Id: I9f4ec7248e3449f9540fc70d60cbdbc3f8cadab0
diff --git a/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java b/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
index a076530..7f50327 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
@@ -66,6 +66,14 @@
     }
 
     /**
+     * Default constructor for Kryo serialization.
+     */
+    protected IpPrefix() {
+        this.address = null;
+        this.prefixLength = 0;
+    }
+
+    /**
      * Returns the IP version of the prefix.
      *
      * @return the IP version of the prefix