[Reviewer: Andy] Use the Diameter Base Accounting application directly, without using the...

... 3GPP Vendor-ID

This matches the definition in TS 32.299, which includes Acct-Application-Id  but excludes Vendor-Specific-Application-Id.

Tested by capturing a CER in Wireshark, and a ACR dump in SAS, and verifying that they had Acct-Application-Id 3 and no Vendor-Specific-Application-Id.

Obv this needs updating.