staging: lustre: ptlrpc: embed highest XID in each request

Atomically assign XIDs and put request and sending list so
we can learn the lowest unreplied XID at any point.

This allows to embed in every resquests the highest XID for
which a reply has been received and does not have an unreplied
lower-numbered XID.

This will be used by the MDT target to release in-memory
reply data corresponding to XIDs of reply received by the client.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Signed-off-by: Gregoire Pichon <gregoire.pichon@bull.net>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5319
Reviewed-on: http://review.whamcloud.com/14793


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>