LU-7525 mdd: mdd_migrate_create() should not set nlink

LU-7525 mdd: mdd_migrate_create() should not set nlink

at object creation. the migration process itself takes
care of nlink incrementing it atomically with dt_insert().

Change-Id: Ia2c8f6cdd77e0808a8060d6e1c542c596612a3ce
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: http://review.whamcloud.com/17496
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Reviewed-by: wangdi <di.wang@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>