code: func NewClient(s *stack.Stack, nicid tcpip.NICID, linkAddr tcpip.LinkAddress, acquiredFunc func(old, new tcpip.Address, cfg Config)) *Client {
  	return &Client{
  		stack:        s,
  		nicid:        nicid,
  		linkAddr:     linkAddr,
  		acquiredFunc: acquiredFunc,
  	}
  }
docs: // NewClient creates a DHCP client.
  //
  // TODO: add s.LinkAddr(nicid) to *stack.Stack.