Merge branch 'conver-net-selftests-to-run-in-unique-namespace-part-1'

Merge branch 'conver-net-selftests-to-run-in-unique-namespace-part-1'

Hangbin Liu says:

====================
Conver net selftests to run in unique namespace (Part 1)

As Guillaume pointed, many selftests create namespaces with very common
names (like "client" or "server") or even (partially) run directly in init_net.
This makes these tests prone to failure if another namespace with the same
name already exists. It also makes it impossible to run several instances
of these tests in parallel.

This patch set intend to conver all the net selftests to run in unique namespace,
so we can update the selftest freamwork to run all tests in it's own namespace
in parallel. After update, we only need to wait for the test which need
longest time.

As the total patch set is too large. I break it to severl parts. This is
the first part.

v2 -> v3:
- Convert all ip netns del to cleanup_ns (Justin Iurman)

v1 -> v2:
- Split the large patch set to small parts for easy review (Paolo Abeni)
- Move busywait from forwarding/lib.sh to net/lib.sh directly (Petr Machata)
- Update setup_ns/cleanup_ns struct (Petr Machata)
- Remove default trap in lib.sh (Petr Machata)
====================

Link: https://lore.kernel.org/r/20231202020110.362433-1-liuhangbin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>