API: Add support for type aliases

Previously all types are compound. This adds support for aliases,
so one can do things like:

typedef u32 interface_index;

or
typedef u8 ip4_address[4];

Change-Id: I0455cad0123fc88acb491d2a3ea2725426bdb246
Signed-off-by: Ole Troan <ot@cisco.com>
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/src/vnet/interface.api b/src/vnet/interface.api
index 2010d8b..84e0483 100644
--- a/src/vnet/interface.api
+++ b/src/vnet/interface.api
@@ -1,5 +1,23 @@
+/* Hey Emacs use -*- mode: C -*- */
+/*
+ * Copyright (c) 2018 Cisco and/or its affiliates.
+ * 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.
+ */
+
 option version = "2.2.0";
 
+import "vnet/interface_types.api";
+
 service {
   rpc want_interface_events returns want_interface_events_reply
     events sw_interface_event;