LU-12273 obd: Reserve metadata overstriping flags

LU-12273 obd: Reserve metadata overstriping flags

Reserve flag bits for metadata overstriping.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <farr0186@gmail.com>
Change-Id: I894b9420a4b08cceaccca6b3184ecb3bd22a680c
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49707
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>