selftests: drv-net: construct environment for running tests which require an endpoint

Nothing surprising here, hopefully. Wrap the variables from
the environment into a class or spawn a netdevsim based env
and pass it to the tests.

Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20240420025237.3309296-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests: drivers: add scaffolding for Netlink tests in Python

Add drivers/net as a target for mixed-use tests.
The setup is expected to work similarly to the forwarding tests.
Since we only need one interface (unlike forwarding tests)
read the target device name from NETIF. If not present we'll
try to run the test against netdevsim.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

selftests: net: add scaffolding for Netlink tests in Python

Add glue code for accessing the YNL library which lives under
tools/net and YAML spec files from under Documentation/.
Automatically figure out if tests are run in tree or not.
Since we'll want to use this library both from net and
drivers/net test targets make the library a target as well,
and automatically include it when net or drivers/net are
included. Making net/lib a target ensures that we end up
with only one copy of it, and saves us some path guessing.

Add a tiny bit of formatting support to be able to output KTAP
from the start.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>