LU-2638 ldiskfs: update dotdot entry for rename

On master, when rename a directory, its old dotdot entry will
be removed firstly, then insert the new dotdot entry, and try
to append FID-in-dirent. But the space for dotdot entry maybe
not enough to hold the new dotdot with FID-in-dirent, such as
the MDT device restored from file-level backup, or the device
is upgraded from 1.8. If we do not move data in the directory
block, the FID-in-dirent will overwrite the dx_root and cause
the directory crashed. Currently, we do not want to introduce
complex logic to handle directory data moving, instead, under
such case, ignore the FID-in-dirent for the new dotdot entry,
and just insert the new dotdot entry.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Id38f5136fb2bc607344c37ca10a32e63ab427e3d
Reviewed-on: http://review.whamcloud.com/5179
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>