def _read_mptcp_fail(self, bits, size):
____ = self._read_fileng(<NUM_LIT:1>)<EOL>dsn_ = self._read_unpack(<NUM_LIT:8>)<EOL>data = dict(<EOL>subtype='<STR_LIT>',<EOL>fail=dict(<EOL>dsn=dsn_,<EOL>),<EOL>)<EOL>return data<EOL>
Read Fallback option.

        Positional arguments:
            * bits - str, 4-bit data
            * size - int, length of option

        Returns:
            * dict -- extracted Fallback (MP_FAIL) option

        Structure of MP_FAIL [RFC 6824]:
                                 1                   2                   3
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
            +---------------+---------------+-------+----------------------+
            |     Kind      |   Length=12   |Subtype|      (reserved)      |
            +---------------+---------------+-------+----------------------+
            |                                                              |
            |                 Data Sequence Number (8 octets)              |
            |                                                              |
            +--------------------------------------------------------------+

            Octets      Bits        Name                    Description
              0           0     tcp.opt.kind            Kind (30)
              1           8     tcp.opt.length          Length (12)
              2          16     tcp.opt.mp.subtype      Subtype (6)
              2          23     -                       Reserved (must be zero)
              4          32     tcp.opt.mp.fail.dsn     Data Sequence Number