Merge branch 'selftests-drv-net-fix-issues-in-devlink_rate_tc_bw-py'

Carolina Jubran says:

====================
selftests: drv-net: Fix issues in devlink_rate_tc_bw.py

This series fixes issues in the devlink_rate_tc_bw.py selftest and
introduces a new Iperf3Runner that helps with measurement handling.
====================

Link: https://patch.msgid.link/20251130091938.4109055-1-cjubran@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>