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.

include/maxscale/server.h

@@ -1,5 +1,6 @@
-#ifndef _SERVER_H
-#define _SERVER_H
+#pragma once
+#ifndef _MAXSCALE_SERVER_H
+#define _MAXSCALE_SERVER_H
 /*
  * Copyright (c) 2016 MariaDB Corporation Ab
  *
@@ -12,6 +13,8 @@
  * of this software will be governed by version 2 or later of the General
  * Public License.
  */
+
+#include <maxscale/cdefs.h>
 #include <maxscale/dcb.h>
 #include <maxscale/resultset.h>
 
@@ -44,6 +47,8 @@
  * @endverbatim
  */
 
+MXS_BEGIN_DECLS
+
 #define MAX_SERVER_NAME_LEN 1024
 #define MAX_NUM_SLAVES 128 /**< Maximum number of slaves under a single server*/
 
@@ -222,4 +227,6 @@ extern RESULTSET *serverGetList();
 extern unsigned int server_map_status(char *str);
 extern bool server_set_version_string(SERVER* server, const char* string);
 
+MXS_END_DECLS
+
 #endif