Specific: NTPHeader().haslayer(NTP) should return True.

def haslayer(self, cls):
        """Specific: NTPHeader().haslayer(NTP) should return True."""
        if cls == "NTP":
            if isinstance(self, NTP):
                return True
        elif issubtype(cls, NTP):
            if isinstance(self, cls):
                return True
        return super(NTP, self).haslayer(cls)