code: func (p *protocol) MinimumPacketSize() int {
  	switch p.number {
  	case ProtocolNumber4:
  		return header.ICMPv4EchoMinimumSize
  	case ProtocolNumber6:
  		return header.ICMPv6EchoMinimumSize
  	}
  	panic(fmt.Sprint("unknown protocol number: ", p.number))
  }
docs: // MinimumPacketSize returns the minimum valid icmp packet size.