ext4: implemet new ioctls to set and get superblock parameters

Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
parameters to be set while the file system is mounted, without needing
write access to the block device.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Message-ID: <20250916-tune2fs-v2-3-d594dc7486f0@mit.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>