LU-7703 mdd: linkea should be updated properly at migration

LU-7703 mdd: linkea should be updated properly at migration

when we're migrating a directory and fix children's linkeas,
do this correctly - search for old fid, replace with a new one.

Change-Id: Ib48f73d51ca635083d733202c59a9bdcdfe116fb
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: http://review.whamcloud.com/18109
Tested-by: Jenkins
Reviewed-by: wangdi <di.wang@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>