ONOS-2728: Define an interface to query about VLAN capability

Change-Id: I53444a7b76902a19548cdac1c557677848a46d1e

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.net.behaviour;
+
+import com.google.common.annotations.Beta;
+import org.onosproject.net.PortNumber;
+import org.onosproject.net.driver.HandlerBehaviour;
+
+/**
+ * A HandlerBehaviour to check the capability of VLAN.
+ */
+@Beta
+public interface VlanQuery extends HandlerBehaviour {
+
+    /**
+     * Indicates if VLAN can be used at the port.
+     *
+     * @param port port to be checked for the capability
+     * @return true if VLAN can be used at the port, false otherwise.
+     */
+    boolean isEnabled(PortNumber port);
+}