opendkim milter does not "ignore" signatures marked as ignore but adds the result dkim=fail in AR header

[futatuki]

libopendkim has a feature that some DKIM-Signature header can be marked as "ignore", however opendkim milter does not care the flag and includes results of those ignored signatures (as "dkim=fail") into Authentication-Results: header.

I think those results should not be included in AR header.

[futatuki]

Per RFC8601 Sec 2.7.1., it seems that we should use dkim=policy in such a case, rather than excluding from AR header.