testsuite: Compliant support for ProDOS Info Bit (PDINFO) in AFP client

[rdmark]

The embedded AFP client in the testsuite don't seem to support the ProDOS info bit properly, in part because of a hackish assumption that PDINFO is always used as the Unicode name offset.

In order to fully test PDINFO, some work on the AFP client will be required.

The original motivation for this is to have tests for ProDOS type/aux to Mac type/creator metadata. Initial effort in PR https://github.com/Netatalk/netatalk/pull/2256 specifically this commit: https://github.com/Netatalk/netatalk/commit/7fb25cee67c9d6a949be5332136a25d501e0fd14