Added events for the Interface subsytem

Change-Id: I9adcc2caa2a98625173c9b9c6d15bbd1a0706eaa
diff --git a/incubator/api/src/main/java/org/onosproject/incubator/net/intf/InterfaceService.java b/incubator/api/src/main/java/org/onosproject/incubator/net/intf/InterfaceService.java
index b164df9..38cfdc5 100644
--- a/incubator/api/src/main/java/org/onosproject/incubator/net/intf/InterfaceService.java
+++ b/incubator/api/src/main/java/org/onosproject/incubator/net/intf/InterfaceService.java
@@ -19,6 +19,7 @@
 import com.google.common.annotations.Beta;
 import org.onlab.packet.IpAddress;
 import org.onlab.packet.VlanId;
+import org.onosproject.event.ListenerService;
 import org.onosproject.net.ConnectPoint;
 
 import java.util.Set;
@@ -27,7 +28,8 @@
  * Service for interacting with interfaces.
  */
 @Beta
-public interface InterfaceService {
+public interface InterfaceService
+        extends ListenerService<InterfaceEvent, InterfaceListener> {
 
     /**
      * Returns the set of all interfaces in the system.