openstack ListAddressesByNetwork op and unit test
diff --git a/openstack/compute/v2/servers/urls.go b/openstack/compute/v2/servers/urls.go
index faa62bd..8998354 100644
--- a/openstack/compute/v2/servers/urls.go
+++ b/openstack/compute/v2/servers/urls.go
@@ -41,3 +41,7 @@
 func listAddressesURL(client *gophercloud.ServiceClient, id string) string {
 	return client.ServiceURL("servers", id, "ips")
 }
+
+func listAddressesByNetworkURL(client *gophercloud.ServiceClient, id, network string) string {
+	return client.ServiceURL("servers", id, "ips", network)
+}