Return True if the packet has a header of the given hdrclass, 
        False otherwise.

def has_header(self, hdrclass):
        '''
        Return True if the packet has a header of the given hdrclass, 
        False otherwise.
        '''
        if isinstance(hdrclass, str):
            return self.get_header_by_name(hdrclass) is not None
        return self.get_header(hdrclass) is not None