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
 +---------------+---------------+-------------------------------+
 |     Type=0x14 |     Length    |           Unassigned          |
 +---------------+---------------+-------------------------------+
 /               Returned Extended TCP header                    /
 /                              ...                              /
 +---------------------------------------------------------------+