GossipHostStore: add AE support

- modified HostDescription family to hold Set of IpAddresses

Change-Id: Id920fdc83817802885e8528af185a5ad590bf999
diff --git a/core/api/src/main/java/org/onlab/onos/net/host/HostDescription.java b/core/api/src/main/java/org/onlab/onos/net/host/HostDescription.java
index fc16854..258ce3d 100644
--- a/core/api/src/main/java/org/onlab/onos/net/host/HostDescription.java
+++ b/core/api/src/main/java/org/onlab/onos/net/host/HostDescription.java
@@ -1,5 +1,7 @@
 package org.onlab.onos.net.host;
 
+import java.util.Set;
+
 import org.onlab.onos.net.Description;
 import org.onlab.onos.net.HostLocation;
 import org.onlab.packet.IpPrefix;
@@ -38,6 +40,6 @@
      * @return host IP address
      */
     // FIXME: Switch to IpAddress
-    IpPrefix ipAddress();
+    Set<IpPrefix> ipAddress();
 
 }