app/testpmd: add host shaper command

app/testpmd: add host shaper command

Add command line options to support host shaper configure.
- Command syntax:
  mlx5 set port <port_id> host_shaper avail_thresh_triggered <0|1> rate
<rate_num>

- Example commands:
To enable avail_thresh_triggered on port 1 and disable current host
shaper:
testpmd> mlx5 set port 1 host_shaper avail_thresh_triggered 1 rate 0

To disable avail_thresh_triggered and current host shaper on port 1:
testpmd> mlx5 set port 1 host_shaper avail_thresh_triggered 0 rate 0

The rate unit is 100Mbps.
To disable avail_thresh_triggered and configure a shaper of 5Gbps on
port 1:
testpmd> mlx5 set port 1 host_shaper avail_thresh_triggered 0 rate 50

Add sample code to handle rxq available descriptor threshold event, it
delays a while so that rxq empties, then disables host shaper and
rearms available descriptor threshold event.

Signed-off-by: Spike Du <spiked@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>