Clarify log message for NODATA/NXDOMAIN without AA

[hlindqvist]

Short description

This adds contextual information to the log message when there is a SOA record in the authority section (typical for NODATA/NXDOMAIN) but the AA flag is not set.

The old log message did not indicate the specific reason why the record was considered irrelevant, logging only information about a SOA record that quite likely is both normal and relevant.

This somewhat helps explaining what the actual problem is.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[rgacogne]

The clang-tidy failure in our CI is unrelated to this change.