LU-4499 nrs: adjust the order of REQ NRS initilization

LU-4499 nrs: adjust the order of REQ NRS initilization

NRS block of ptlrpc_request must be initialized before it is added
into exp_{hp,reg}_list; otherwise ptlrpc_nrs_req_hp_move() may access
uninitialized NRS block. Code cleanup.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: Ide1d7edfa5e09bf498baaa60023dbccf3fb152dc
Reviewed-on: http://review.whamcloud.com/15943
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>