test: DTN7: Specify AAP 2.0 socket explicitly
As we do not allow reuse of the same socket file by concurrently running uD3TN instances, uD3TN may crash on startup if we do not use different socket filenames.
See: https://gitlab.com/d3tn/ud3tn/-/jobs/5740147850#L232 See: #156 (closed) Closes: #164 (closed)