ext4: show 'shutdown' hint when ext4 is forced to shutdown

ext4: show 'shutdown' hint when ext4 is forced to shutdown

Now, if dmesg is cleared, we have no way of knowing if the file system has
been shutdown. Moreover, ext4 allows directory reads even after the file
system has been shutdown, so when reading a file returns -EIO, we cannot
determine whether this is a hardware issue or if the file system has been
shutdown.

Therefore, when ext4 file system is shutdown, we're adding a 'shutdown'
hint to commands like mount so users can easily check the file system's
status.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250122114130.229709-8-libaokun@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>