This is a follow up from !7805 (merged) to add more tests for the source-port configuration.
To quote @pspacek:
Well, this is pretty large change and needs tests. If nothing else I would like to see what happens if:
- attempt to open TCP connection ends up in packet black-hole
- connection is established and the remote side does not respond (established connection hangs)
- the remote side responds with some something which does not parse as DNS
- the remote side sends mismatching NOTIFY answer (say different zone name)