LU-14526 flr: mirror split downgrade SOM

LU-14526 flr: mirror split downgrade SOM

After mirror split, the file's blocks on SoM is not accurate, this
patch downgrade the SoM from STRICT so that size glimpse does not
trust the SoM from the MDS.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I02350c24190d96af93fed8c1b8a0bc6beb2c4bc2
Reviewed-on: https://review.whamcloud.com/43168
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>