s4:auth: a simple bind uses the DCs name as workstation

s4:auth: a simple bind uses the DCs name as workstation

I've seen that in LogonSamLogonEx request triggered
by a simple bind with a user of a trusted domain
within the same forest. Note simple binds don't
work with users for another forest/external domain,
as the DsCrackNames call on the bind_dn fails.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13879
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14641

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>