Merge branch 'selftests-fib_rule_tests-cleanups-and-new-tests'

Ido Schimmel says:

====================
selftests: fib_rule_tests: Cleanups and new tests

This patchset performs some cleanups and adds new tests in preparation
for upcoming FIB rule DSCP selector.
====================

Link: https://patch.msgid.link/20240814111005.955359-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>