cache: move setting EDE "Stale Answer" to the the serve_stale module.
Just calling stale_cb
doesn't guarantee that the request will finish in state DONE.
This prevents other EDE codes from being applied to the request and in case the request ends in FAIL state it produces a SERVFAIL answer with EDE "Stale Answer", which is a bit weird.
Move setting EDEs in answer_finalize in the serve_stale module, where the proper EDE in case of NXDOMAIN is set too.
Edited by menakite