winbind pam-config: fix account section
This fixes a bug[1], where the PAM "account" part will never be executed because the pam_unix usually return success due the presence of the nss-winbind library.
The bug reporter points to sssd, how the problem is solved there, by making the account section of type "Additional". This way pam_winbind is always executed and i.e. enforces users with expired passwords to change it before logging in.
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=907318