Generates the next RadioTapExtendedPresenceMask

def _next_radiotap_extpm(pkt, lst, cur, s):
    """Generates the next RadioTapExtendedPresenceMask"""
    if cur is None or (cur.present and cur.present.Ext):
        st = len(lst) + (cur is not None)
        return lambda *args: RadioTapExtendedPresenceMask(*args, index=st)
    return None