code: func (e *endpoint) maxOptionSize() (size int) {
  	var maxSackBlocks [header.TCPMaxSACKBlocks]header.SACKBlock
  	options := e.makeOptions(maxSackBlocks[:])
  	size = len(options)
  	putOptions(options)
  
  	return size
  }
docs: // maxOptionSize return the maximum size of TCP options.