Replaced the usage of IpPrefix with IpAddress in the context of
Controller Nodes.

Change-Id: Id2b25fb071bb20541db3f77b7afefe886520538e
diff --git a/core/api/src/main/java/org/onlab/onos/cluster/ControllerNode.java b/core/api/src/main/java/org/onlab/onos/cluster/ControllerNode.java
index 33fe1c9..00e3346 100644
--- a/core/api/src/main/java/org/onlab/onos/cluster/ControllerNode.java
+++ b/core/api/src/main/java/org/onlab/onos/cluster/ControllerNode.java
@@ -1,6 +1,6 @@
 package org.onlab.onos.cluster;
 
-import org.onlab.packet.IpPrefix;
+import org.onlab.packet.IpAddress;
 
 /**
  * Represents a controller instance as a member in a cluster.
@@ -33,7 +33,7 @@
      *
      * @return IP address
      */
-    IpPrefix ip();
+    IpAddress ip();
 
 
     /**