MXS-2550: Fix default module parameters

The parameters weren't processed when they were added from the module
defaults.

server/core/config.cc

@@ -3638,6 +3638,7 @@ void config_add_defaults(CONFIG_CONTEXT* ctx, const MXS_MODULE_PARAM* params)
             {
                 bool rv = config_add_param(ctx, params[i].name, params[i].default_value);
                 MXS_ABORT_IF_FALSE(rv);
+                config_fix_param(params, config_get_param(ctx->parameters, params[i].name));
             }
         }
     }