code: func TCPFlags(flags uint8) TransportChecker {
  	return func(t *testing.T, h header.Transport) {
  		t.Helper()
  
  		tcp, ok := h.(header.TCP)
  		if !ok {
  			return
  		}
  
  		if f := tcp.Flags(); f != flags {
  			t.Errorf("Bad flags, got 0x%x, want 0x%x", f, flags)
  		}
  	}
  }
docs: // TCPFlags creates a checker that checks the tcp flags.