test_service_sctp_ping or test_service_udp_ping tests are failing with:

testtools.matchers._impl.MismatchError: 2 != 0: Incorrect amount of unique backends. Got set()

This doesn't appear to affect TCP variation of this test.
Investigations
I found that while we're calling the UDP server with 5 seconds timeout waiting for a response, we're only waiting 2 seconds for the result of the `kubectl exec`. This is out of sync. Unfortunately the patch bumping the time to 10 seconds doesn't really help with the SCTP test.

Moreover, when testing I tried to put a sleep into the UDP server, yet I couldn't reproduce the issue, suggesting that it might be even more complicated.
Root cause
Solution
Increase timeout, which should help UDP tests: https://review.opendev.org/c/openstack/kuryr-tempest-plugin/+/831944