for consistency, add Message-Authenticator for PAP authentication, too

[restena-sw]

The code sets the Message-Authenticator attribute for MSCHAP and EAP-MSCHAPv2 but not for simple PAP.

While per RFC Message-Authenticator is optional for PAP, many clients and servers set it as a BCP.

So, how about adding one single LOC with a ->setIncludeMessageAuthenticator() in the PAP authentication function?