LU-10213 lnd: calculate qp max_send_wrs properly

LU-10213 lnd: calculate qp max_send_wrs properly

The maximum in-flight transfers can not exceed the
negotiated queue depth. Instead of calculating the
max_send_wrs to be the negotiated number of frags *
concurrent sends, it should be the negotiated number
of frags * queue depth.

If that value is too large for successful qp creation then
we reduce the queue depth in a loop until we successfully
create the qp or the queue depth dips below 2.

Due to the queue depth negotiation protocol it is guaranteed
that the queue depth on both the active and the passive
will match.

This change resolves the discrepancy created by the previous
code which reduces max_send_wr by a quarter.

That could lead to:
mlx5_ib_post_send:4184:(pid 26272): Failed to prepare WQE
When the o2iblnd transfers a message which requires more
WRs than the max that has been allocated.

Test-Parameters: trivial
Signed-off-by: Alexey Lyashkov <alexey.lyashkov@seagate.com>
Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Change-Id: I88f96f950bf4c0a8efd4df812d44e5e20d5907dc
Reviewed-on: https://review.whamcloud.com/30310
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Doug Oucharek <dougso@me.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>