libwbclient: Re-Fix a bug that was fixed with e5741e27c4c

libwbclient: Re-Fix a bug that was fixed with e5741e27c4c

> r21878: Fix a bug with smbd serving a windows terminal server: If winbind
> decides smbd to be idle it might happen that smbd needs to do a winbind
> operation (for example sid2name) as non-root. This then fails to get the
> privileged pipe. When later on on the same connection another authentication
> request comes in, we try to do the CRAP auth via the non-privileged pipe.
>
> This adds a winbindd_priv_request_response() request that kills the existing
> winbind pipe connection if it's not privileged.

The fix for this was lost during the conversion to libwbclient.

Thanks to Ira Cooper <samba@ira.wakeful.net> for pointing this out!

Volker