selftests: nic_performance: Add selftest for performance of NIC driver

Add selftest case to check the send and receive throughput.
Supported link modes between local NIC driver and partner
are varied. Then send and receive throughput is captured
and verified. Test uses iperf3 tool.
Add iperf3 server/client function in GenerateTraffic class.

Signed-off-by: Mohan Prasad J <mohan.prasad@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>