Bug#37061960 : InnoDB redo recovery failure/corruption due to INSTANT ddl.+ innodb col limits

Symptom :
  - Maximum number of user columns in a table supported in InnoDB is 1017.
  - Metadata of Columns, dropped with ALGORITHM=INSTANT, is kept and these
    columns are also counted in that limit of 1017.
  - With DROP and ADD colimn combination, it was possible to have number of
    columns cross maximum allowed column limit.
  - And there were assertion failures during recovery during replaying the
    INSERT opertation on this table.
  - This is a boundary case.

Root cause:
  - We try to make sure to limit the total number of columns within limit.
  - But while checking maximum number of columns REC_MAX_N_FIELDS is used.
    REC_MAX_N_FIELDS value is 1023 (1017 + 6).
  - 6 is for twice the number of system columns (DATA_N_SYS_COLS).
  - These system cols are DB_ROW_ID, DB_TRX_ID, DB_ROLL_PTR.
  - why twice? Code comments says the following :
   "
    We need "* 2" because mlog_parse_index() creates a dummy table object
    possibly, with some of the system columns in it, and then adds the 3
    system columns (again) using dict_table_add_system_columns(). The problem
    is that mlog_parse_index() cannot recognize the system columns by
    just having n_fields, n_uniq and the lengths of the columns.
   "

Fix :
  In check_if_supported_inplace_alter, correct the check for maximum possible
  columns to keep it within 1017.

Change-Id: I9d6c3183373b8acb269fe6ac6fb2e2bb2a0495ed

Author: mayprasa