Fix NETLOGON credential chain with Windows 2008 all over the place.

Fix NETLOGON credential chain with Windows 2008 all over the place.

In order to avoid receiving NT_STATUS_DOWNGRADE_DETECTED from a w2k8
netr_ServerAuthenticate2 reply, we need to start with the AD netlogon negotiate
flags everywhere (not only when running in security=ads). Only for NT4 we need
to do a downgrade to the returned negotiate flags.

Tested with w2k8, w2ksp4, w2k3r2 and nt4sp6.

Guenther
(This used to be commit 0970369ca0cb9ae465cff40e5c75739824daf1d0)