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/protocol/HTTPD/httpd.c

@@ -32,6 +32,8 @@
  * @endverbatim
  */
 
+#define MXS_MODULE_NAME "HTTPD"
+
 #include "httpd.h"
 #include <ctype.h>
 #include <maxscale/alloc.h>