ext4: reflect mb_optimize_scan value in options file

Add support to display the mb_optimize_scan value in
/proc/fs/ext4/<dev>/options file. The option is only
displayed when the value is non default.

Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20220704054603.21462-1-ojaswin@linux.ibm.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>