LU-15692 lmv: change default hash back to fnv_1a_64

LU-15692 lmv: change default hash back to fnv_1a_64

Until performance issue is resolved, change the default directory
hash type from 'crush' back to 'fnv_1a_64'.

Fixes: bb60caa1c6e7 ("LU-14459 lmv: change default hash type to crush")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: If2cef70298773f42dc1c62809eea98519b3ebbe5
Reviewed-on: https://review.whamcloud.com/46950
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Shuichi Ihara <sihara@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>