LU-3453 mdt: check for packed reply in mdt_intent_opc()

In mdt_intent_opc() check that the reply has been packed before trying
to adjust the lock policy result.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Iab2858bf26390e6c305fcca6b7b7e0bc1be32a71
Reviewed-on: http://review.whamcloud.com/6617
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>