Merge branch 'selftests-drv-net-support-testing-with-a-remote-system'

Jakub Kicinski says:

====================
selftests: drv-net: support testing with a remote system

Implement support for tests which require access to a remote system /
endpoint which can generate traffic.
This series concludes the "groundwork" for upstream driver tests.

I wanted to support the three models which came up in discussions:
 - SW testing with netdevsim
 - "local" testing with two ports on the same system in a loopback
 - "remote" testing via SSH
so there is a tiny bit of an abstraction which wraps up how "remote"
commands are executed. Otherwise hopefully there's nothing surprising.

I'm only adding a ping test. I had a bigger one written but I was
worried we'll get into discussing the details of the test itself
and how I chose to hack up netdevsim, instead of the test infra...
So that test will be a follow up :)

v4: https://lore.kernel.org/all/20240418233844.2762396-1-kuba@kernel.org
v3: https://lore.kernel.org/all/20240417231146.2435572-1-kuba@kernel.org
v2: https://lore.kernel.org/all/20240416004556.1618804-1-kuba@kernel.org
v1: https://lore.kernel.org/all/20240412233705.1066444-1-kuba@kernel.org
====================

Link: https://lore.kernel.org/r/20240420025237.3309296-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>