Merge branch 'selftests-net-use-slowwait-to-make-sure-setup-finished'

Hangbin Liu says:

====================
selftests: net: use slowwait to make sure setup finished

The two updated tests sometimes failed because the network setup hadn't
completed. Used slowwait to ensure the setup finished and the tests
always passed. I ran both tests 50 times, and all of them passed.
====================

Link: https://patch.msgid.link/20250617105101.433718-1-liuhangbin@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>