Merge branch 'selftests-tc-testing-updates-and-cleanups-for-tdc'

Pedro Tammela says:

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selftests: tc-testing: updates and cleanups for tdc

Address the recommendations from the previous series and cleanup some
leftovers.
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Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>