Merge branch 'selftests-net-lib-small-fixes'

Matthieu Baerts says:

====================
selftests: net: lib: small fixes

While looking at using 'lib.sh' for the MPTCP selftests [1], we found
some small issues with 'lib.sh'. Here they are:

- Patch 1: fix 'errexit' (set -e) support with busywait. 'errexit' is
  supported in some functions, not all. A fix for v6.8+.

- Patch 2: avoid confusing error messages linked to the cleaning part
  when the netns setup fails. A fix for v6.8+.

- Patch 3: set a variable as local to avoid accidentally changing the
  value of a another one with the same name on the caller side. A fix
  for v6.10-rc1+.

Link: https://lore.kernel.org/mptcp/5f4615c3-0621-43c5-ad25-55747a4350ce@kernel.org/T/
====================

Link: https://lore.kernel.org/r/20240605-upstream-net-20240605-selftests-net-lib-fixes-v1-0-b3afadd368c9@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>