LU-7536 mdt: handling NULL dereference in mdt_reconstruct

LU-7536 mdt: handling NULL dereference in mdt_reconstruct

mdt_reconstruct function corresponding to op-code
REINT_MIGRATE is not present, so as per request format
used in mdt_reint adding mdt reconstruct functions.
Also added assertion to check max opcodes and undefined
reconstruct function. Also updated opcode REINT_RMENTRY
and REINT_MIGRADE at missing places.

Seagate-bug-id: MRP-3205
Signed-off-by: Jadhav Vikram <jadhav.vikram@seagate.com>
Change-Id: I489ee3dfa5972c14f37aed5307103cf329d802f7
Reviewed-on: http://review.whamcloud.com/20395
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>