f2fs: issue all big range discards in umount process

This patch modify max_requests to UINT_MAX, to issue
all big range discards in umount.

Signed-off-by: Yunlei He <heyunlei@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -943,6 +943,7 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
 	} else if (discard_type == DPOLICY_FSTRIM) {
 		dpolicy->io_aware = false;
 	} else if (discard_type == DPOLICY_UMOUNT) {
+		dpolicy->max_requests = UINT_MAX;
 		dpolicy->io_aware = false;
 	}
 }