ONOS-6887 Move neighbour classes from incubator to core

Change-Id: I5fa70253b833838566a3527d8938e04be4274210
diff --git a/core/api/src/main/java/org/onosproject/net/neighbour/NeighbourMessageHandler.java b/core/api/src/main/java/org/onosproject/net/neighbour/NeighbourMessageHandler.java
new file mode 100644
index 0000000..040f4b0
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/neighbour/NeighbourMessageHandler.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2016-present Open Networking Foundation
+ *
+ * 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.neighbour;
+
+import com.google.common.annotations.Beta;
+import org.onosproject.net.host.HostService;
+
+/**
+ * Handler for an incoming neighbour message.
+ *
+ * <p>An application may implement this interface in order to provide their own
+ * logic for handling particular neighbour messages.</p>
+ */
+@Beta
+public interface NeighbourMessageHandler {
+
+    /**
+     * Handles a neighbour message.
+     *
+     * @param context neighbour message context
+     * @param hostService host service
+     */
+    void handleMessage(NeighbourMessageContext context, HostService hostService);
+}