Include MariaDB Connector-C headers first

The MariaDB Connector-C headers that are built by MaxScale must be
included before any system headers.

Fixed code that explicitly included the <mysql.h> header to use the
<maxscale/protocol/mysql.h> wrapper instead.

include/maxscale/mysql_utils.h

@@ -15,7 +15,7 @@
 #include <maxscale/cdefs.h>
 #include <stdlib.h>
 #include <stdint.h>
-#include <mysql.h>
+#include <maxscale/protocol/mysql.h>
 #include <maxscale/server.h>
 
 MXS_BEGIN_DECLS