staging/lustre/hsm: HSM requests not delivered

The total size of an HSM archive request may exceed the
desired (LNET) message. When this happens, it can hang
the client and not allow the archive request to succeed.

Before we know the total size of the hsm_action_items, we
need to limit the size of the reguest. Doing this limits
the number of items that can be sent in one archive request.
We'e reduced the size allowed for the user archive request
to MDS_MAXREQSIZE/3.

Signed-off-by: James Nunez <james.a.nunez@intel.com>
Reviewed-on: http://review.whamcloud.com/9393
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4639


Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>