TG is reporting dropped packets for all rates during binary search of NDR.

Dropped packet means either malformed packets (dropped by NIC) or packet dropped by vpp.
PERF test are using 3-node topology:
TG - DUT1 - DUT2 - TG
Traffic streams
stream1: (TG)port1 -> DUT1 -> DUT2 -> port2(TG)
stream2: (TG)port2 -> DUT2 -> DUT1 -> port1(TG)

each stream has ~252 flows (incrementing src_ip)

observations:

• This happens randomly in 1 out of 200 test runs, mostly with multithreaded vpp.
• packet loss reported by TG only in one direction
• numbers of ierrors reported by TG is aproximately 2*packet lost count

example of failure: https://jenkins.fd.io/view/csit/job/csit-vpp-perf-1606-all/

stats from test "4core VPP with rss 2 passes 1518B frames through IPv4 forwarding with COP at 2x 812,743pps in 3-node topology" attached