code: func ConnectionManager(connman ifconnmgr.ConnManager) Option {
  	return func(cfg *Config) error {
  		if cfg.ConnManager != nil {
  			return fmt.Errorf("cannot specify multiple connection managers")
  		}
  		cfg.ConnManager = connman
  		return nil
  	}
  }
docs: // ConnectionManager configures libp2p to use the given connection manager.