LU-10988 lfsck: load object attr when prepare LFSCK request

It will avoid empty attrs in LFSCK request (lfsck_namespace_req).
The patch also shows invalid mode for dt_mode_to_dft() for debug.

Other cleanup for lfsck_namespace_striped_dir_rescan().

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I2874160d9a0c9e3084d0d3d7f365940108c82018
Reviewed-on: https://review.whamcloud.com/32245


Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>