selftests: tc-testing: move back to per test ns setup

selftests: tc-testing: move back to per test ns setup

Surprisingly in kernel configs with most of the debug knobs turned on,
pre-allocating the test resources makes tdc run much slower overall than
when allocating resources on a per test basis.

As these knobs are used in kselftests in downstream CIs, let's go back
to the old way of doing things to avoid kselftests timeouts.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202311161129.3b45ed53-oliver.sang@intel.com
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20231117171208.2066136-3-pctammela@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>