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