In reverse-ordered column families, if one wants to start reading at the
  logical end of the index, they should Seek() to a key value that is not
  covered by the index. This may (and typically does) prevent use of a bloom
  filter.
  The calls to setup_scan_iterator() that are made for index and table scan
  didn't take this into account and passed eq_cond_len=INDEX_NUMBER_SIZE.
  Fixed them to compute and pass correct eq_cond_len.

  Also, removed an incorrect assert in ha_rocksdb::setup_iterator_bounds.