f2fs: deliver the accumulated 'issued' to __issue_discard_cmd_orderly()

Any of the following scenarios will send more than the number of
max_requests at a time, which will not meet the design of the
max_requests limit.

- Set max_ordered_discard larger than discard_granularity from userspace.
- It is a small size device, discard_granularity can be tuned to 1 in
  f2fs_tuning_parameters().

We need to deliver the accumulated @issued to __issue_discard_cmd_orderly()
to meet the max_requests limit.

BTW, convert the parameter type of @issued in __submit_discard_cmd().

Signed-off-by: Yuwei Guan <Yuwei.Guan@zeekrlife.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>