Our NetperfSession class only allows for a single Netperf process to be run at a time. However, multiple simultaneous Netperf runs allow for more interesting and realistic testing scenarios involving multiple flows (latency under load, total throughput vs number of flows, etc).

This change would also require modifying NetperfRunner to allow for manual specification of the port number used by Netperf/Netserver to effectively simulate multiple flows (when receive/transmit-side scaling is based on (src IP, src port, dst IP, dst port) tuples, this would be necessary to test network scaling).