def _read_mptcp_prio(self, bits, size):
        """Read Change Subflow Priority option.

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

        Returns:
            * dict -- extracted Change Subflow Priority (MP_PRIO) option

        Structure of MP_PRIO [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    |Subtype|     |B| AddrID (opt) |
            +---------------+---------------+-------+-----+-+--------------+

            Octets      Bits        Name                    Description
              0           0     tcp.opt.kind            Kind (30)
              1           8     tcp.opt.length          Length (3/4)
              2          16     tcp.opt.mp.subtype      Subtype (5)
              2          23     tcp.opt.mp.prio.backup  Backup Path (B)
              3          24     tcp.opt.mp.prio.addrid  Address ID (optional)

        """
        temp = self._read_unpack(1) if size else None

        data = dict(
            subtype='MP_PRIO',
            prio=dict(
                res=b'\x00' * 3,
                backup=True if int(bits[3]) else False,
                addrid=temp,
            ),
        )

        return data
Read Change Subflow Priority option.

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

        Returns:
            * dict -- extracted Change Subflow Priority (MP_PRIO) option

        Structure of MP_PRIO [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    |Subtype|     |B| AddrID (opt) |
            +---------------+---------------+-------+-----+-+--------------+

            Octets      Bits        Name                    Description
              0           0     tcp.opt.kind            Kind (30)
              1           8     tcp.opt.length          Length (3/4)
              2          16     tcp.opt.mp.subtype      Subtype (5)
              2          23     tcp.opt.mp.prio.backup  Backup Path (B)
              3          24     tcp.opt.mp.prio.addrid  Address ID (optional)