ext4, doc: fix incorrect h_reserved size

stable inclusion
from stable-v5.10.113
commit 0c54b093766becb9c83317232c93290cf612b8ff
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5ISAH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c54b093766becb9c83317232c93290cf612b8ff



--------------------------------

commit 7102ffe4 upstream.

According to document and code, ext4_xattr_header's size is 32 bytes, so
h_reserved size should be 3.

Signed-off-by: Wang Jianjian <wangjianjian3@huawei.com>
Link: https://lore.kernel.org/r/92fcc3a6-7d77-8c09-4126-377fcb4c46a5@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>