LU-13666 lod: update .do_index_ops on layout detach

LU-13666 lod: update .do_index_ops on layout detach

Directory migration detaches stripes from source, and then attaches
them to target if source is a striped directory. This will convert
source from striped directory to plain directory, it needs update
.do_index_ops from lod_striped_index_ops to lod_index_ops to avoid
trigger assertion in index ops.

Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: Ia8f66a8a3fd5e96f0dba4d60eb2443107d320418
Reviewed-on: https://review.whamcloud.com/39226
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>