code: func (ecmd *EthtoolCmd) CmdSet(intf string) (uint32, error) {
  	e, err := NewEthtool()
  	if err != nil {
  		return 0, err
  	}
  	defer e.Close()
  	return e.CmdSet(ecmd, intf)
  }
docs: // CmdSet sets and returns the settings in the receiver struct
  // and returns speed