Cleanup header files

- All now include maxscale/cdefs.h as the very first file.
- MXS_[BEGIN|END]_DECLS added to all C-headers.
  Strictly speaking not necessary for private headers, but
  does not hurt either.
- Include guards moved to the very top of the file.
- #pragma once added.

server/modules/routing/avro/avrorouter.h

@@ -1,3 +1,6 @@
+#pragma once
+#ifndef _MXS_AVRO_H
+#define _MXS_AVRO_H
 /*
  * Copyright (c) 2016 MariaDB Corporation Ab
  *
@@ -15,8 +18,7 @@
  * MaxScale AVRO router
  *
  */
-#ifndef _MXS_AVRO_H
-#define _MXS_AVRO_H
+#include <maxscale/cdefs.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <blr_constants.h>
@@ -35,6 +37,8 @@
 #include <sqlite3.h>
 #include <maxscale/protocol/mysql.h>
 
+MXS_BEGIN_DECLS
+
 /** SQLite3 version 3.7.14 introduced the new v2 close interface */
 #if SQLITE_VERSION_NUMBER < 3007014
 #define sqlite3_close_v2 sqlite3_close
@@ -312,4 +316,6 @@ extern void table_map_remap(uint8_t *ptr, uint8_t hdr_len, TABLE_MAP *map);
 #define AVRO_CS_BUSY             0x0001
 #define AVRO_WAIT_DATA           0x0002
 
+MXS_END_DECLS
+
 #endif