Implement default method for isConfigured

Change-Id: I30058a186d92b291f0334834fbe3679e30fd247c
diff --git a/core/api/src/main/java/org/onosproject/net/intf/InterfaceService.java b/core/api/src/main/java/org/onosproject/net/intf/InterfaceService.java
index 09743df..2e5f4ec 100644
--- a/core/api/src/main/java/org/onosproject/net/intf/InterfaceService.java
+++ b/core/api/src/main/java/org/onosproject/net/intf/InterfaceService.java
@@ -18,6 +18,7 @@
 
 import java.util.Set;
 
+import org.apache.commons.lang.NotImplementedException;
 import org.onlab.packet.IpAddress;
 import org.onlab.packet.VlanId;
 import org.onosproject.event.ListenerService;
@@ -95,5 +96,7 @@
      * @param connectPoint the port on a device
      * @return true if connectpoint has a configured interface
      */
-    boolean isConfigured(ConnectPoint connectPoint);
+    default boolean isConfigured(ConnectPoint connectPoint) {
+        throw new NotImplementedException("isConfigured is not implemented");
+    }
 }