LU-9121 lnet: Add the userspace De-Marshalling API

LU-9121 lnet: Add the userspace De-Marshalling API

Given a bulk containing a single UDSP, De-Marshalling
API demarshals it and populates a udsp structure.

Change-Id: Id2502dffc6fd259ad552c018b0cab415a12a8cfe
Test-Parameters: trivial testlist=lnet-selftest,sanity-lnet
Signed-off-by: Sonia Sharma <sharmaso@whamcloud.com>
Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34501
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>