Move module object inside MODULE_INFO

This allows modules to only expose one entry point with a consistent
signature. In the future, this could be used to implement declarations of
module parameters.

include/maxscale/modinfo.h

@@ -86,6 +86,7 @@ typedef struct
     MODULE_VERSION  api_version;
     const char     *description;
     const char     *version;
+    void           *module_object;
 } MODULE_INFO;
 
 MXS_END_DECLS