Add definitions of MXS_MODULE_NAME to all modules

All modules now declare a name for the module. This is name is added as a
prefix to all messages logged by a module. The prefix should help
determine which part of the system logs a message.

server/modules/routing/avrorouter/avro_schema.c

@@ -14,11 +14,9 @@
 /**
  * @file avro_schema.c - Avro schema related functions
  */
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE
-#endif
 
 #include "avrorouter.h"
+
 #include <maxscale/mysql_utils.h>
 #include <jansson.h>
 #include <stdio.h>