ONOS-2926 Adding unit test to verify removeIp in ECHostStore

Change-Id: I9606b4cbfc440e5c03186031eba5ec1a97326569
diff --git a/core/store/dist/src/main/java/org/onosproject/store/host/impl/ECHostStore.java b/core/store/dist/src/main/java/org/onosproject/store/host/impl/ECHostStore.java
index 26c6a84..4d3cc6a 100644
--- a/core/store/dist/src/main/java/org/onosproject/store/host/impl/ECHostStore.java
+++ b/core/store/dist/src/main/java/org/onosproject/store/host/impl/ECHostStore.java
@@ -206,8 +206,9 @@
                 checkState(Objects.equals(hostId.vlanId(), existingHost.vlan()),
                         "Existing and new VLANs differ.");
 
-                Set<IpAddress> addresses = new HashSet<>(existingHost.ipAddresses());
+                Set<IpAddress> addresses = existingHost.ipAddresses();
                 if (addresses != null && addresses.contains(ipAddress)) {
+                    addresses = new HashSet<>(existingHost.ipAddresses());
                     addresses.remove(ipAddress);
                     return new DefaultHost(existingHost.providerId(),
                             hostId,