docs: filesystems: f2fs: fix description about compress ioctl

Since commit c6140415 ("f2fs: introduce FI_COMPRESS_RELEASED
instead of using IMMUTABLE bit"), we no longer use the IMMUTABLE
bit to prevent writing data for compression. Let's correct the
corresponding documentation.

BTW, this patch fixes some alignment issues in the compress
metadata layout.

Signed-off-by: Chao Liu <liuchao@coolpad.com>
Link: https://lore.kernel.org/r/20220613020800.3379482-1-chaoliu719@gmail.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>