code: func DstAddr(addr tcpip.Address) NetworkChecker {
  	return func(t *testing.T, h []header.Network) {
  		t.Helper()
  
  		if a := h[0].DestinationAddress(); a != addr {
  			t.Errorf("Bad destination address, got %v, want %v", a, addr)
  		}
  	}
  }
docs: // DstAddr creates a checker that checks the destination address.