message: op-node: Fix log level handler
  The handler returned from `log.LvlFilterHandler` wasn't being consumed anywhere, so log level configuration was being ignored.
diff: @@ -44,7 +44,7 @@ func (cfg *LogConfig) Check() error {
  func (cfg *LogConfig) NewLogger() log.Logger {
  handler := log.StreamHandler(os.Stdout, format(cfg.Format, cfg.Color))
  handler = log.SyncHandler(handler)
  - log.LvlFilterHandler(level(cfg.Level), handler)
  + handler = log.LvlFilterHandler(level(cfg.Level), handler)
  logger := log.New()
  logger.SetHandler(handler)
  return logger
  