vdpa/mlx5: workaround FW first completion in start

vdpa/mlx5: workaround FW first completion in start

After a vDPA application restart, Qemu restores VQ with used and
available index, new incoming packet triggers virtio driver to
handle buffers. Under heavy traffic, no available buffer for
firmware to receive new packets, no Rx interrupts generated,
driver is stuck on endless interrupt waiting.

As a firmware workaround, this patch sends a notification after
VQ setup to ask driver handling buffers and filling new buffers.

Fixes: bff735011078 ("vdpa/mlx5: prepare virtio queues")
Cc: stable@dpdk.org
Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Reviewed-by: Matan Azrad <matan@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>