Merge branch 'selftests-drv-net-convert-so_txtime-to-drv-net'

Willem de Bruijn says:

====================
selftests: drv-net: convert so_txtime to drv-net

In preparation for extending to pacing hardware offload, convert the
so_txtime.sh test to a drv-net test that can be run against netdevsim
and real hardware.

Two preparatory patches
1. support negative tests, where tests are expected to fail
2. add a tc helper

See individual patches for details and detailed changelog
====================

Link: https://patch.msgid.link/20260504174056.565319-1-willemdebruijn.kernel@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>