backend/ipp: Fix report_attr() to handle localized and octetString IPP tags

[g0r3]

I've started using the the IPP Everywhere driver with my Brother MFC-L3750CDW, as I had problems using the proprietary driver on Nixos. And while IPP Everywhere resolves that problem and works great for printing, I found that it doesn't provide the toner status.

lpstat showed no toner levels even though ipptool showed the data was there. I have programming experience, but I am not a versed C guy, so I used the help of an LLM to trace the code path and identify the problem. Not sure if this is accepted.

The error description and fix according to the LLM:

What's happening

ippFindAttribute() correctly matches localized types to their base
types (e.g., NAMELANG → NAME) in cups/ipp.c. But report_attr()
switches on attr->value_tag (the actual tag, e.g., NAMELANG), and
its switch only covers INTEGER, TEXT, NAME, and KEYWORD. The
unhandled tag falls through to default: return;, silently dropping
the data.

Fix

Add IPP_TAG_TEXTLANG, IPP_TAG_NAMELANG, and IPP_TAG_STRING as
fall-through cases. They use the same string.text union member, so
no additional logic is needed.

I've tested the patch locally with my Brother MCF-L3750CDW with IPP Everywhere.
After applying the patch the toner levels are correctly reported in lpstat and (in my case) the KDE printer settings.

[michaelrsweet]

OK, so first you can't use string.text for IPP_TAG_STRING because that syntax is a binary string that can contain nul characters.

Will review this in more detail when I have a chance...

[g0r3]

OK, thanks for the heads-up. I've removed it from the fall-through cases.