LU-8250 mdd: move linkea prepare out of transaction.

LU-8250 mdd: move linkea prepare out of transaction.

Move linkea prepare out of transaction to avoid reading
linkea remotely inside the transaciton.

Signed-off-by: Di Wang <di.wang@intel.com>
Change-Id: I10f0979c0c496fdcc5349f36ac5cca123d42c8a5
Reviewed-on: http://review.whamcloud.com/23096
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>