code: func (s *Stack) AddLinkAddress(nicid tcpip.NICID, addr tcpip.Address, linkAddr tcpip.LinkAddress) {
  	fullAddr := tcpip.FullAddress{NIC: nicid, Addr: addr}
  	s.linkAddrCache.add(fullAddr, linkAddr)
  	// TODO: provide a way for a transport endpoint to receive a signal
  	// that AddLinkAddress for a particular address has been called.
  }
docs: // AddLinkAddress adds a link address to the stack link cache.