code: func (b IPv6) IsValid(pktSize int) bool {
  	if len(b) < IPv6MinimumSize {
  		return false
  	}
  
  	dlen := int(b.PayloadLength())
  	if dlen > pktSize-IPv6MinimumSize {
  		return false
  	}
  
  	return true
  }
docs: // IsValid performs basic validation on the packet.