Extend DsBind and DsGetDomainControllerInfo to work with w2k8.

Extend DsBind and DsGetDomainControllerInfo to work with w2k8.

W2K8 Clients ask for DRSUAPI_SUPPORTED_EXTENSION_LH_BETA2 on DsBind. W2K8
expect this to be set (with server fl 2k8) or else they do not call
DsGetDomainControllerInfo.

If DRSUAPI_SUPPORTED_EXTENSION_LH_BETA2 is set, DsGetDomainControllerInfo
must be able to return DCInfo Level 3.

If Samba4 AD ist set to work as 2k8, with >2k8 clients the following
will not work as expected:

  * Group Policy Editor Infrastructure Discovery
  * nltest /dclist:<domain>
  * w32tm /monitor

BUG: https://bugzilla.samba.org/show_bug.cgi?id=9971
BUG: https://bugzilla.samba.org/show_bug.cgi?id=9976

Signed-off-by: Dirk Godau <voidswitch@gmail.com>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Autobuild-User(master): Douglas Bagnall <dbagnall@samba.org>
Autobuild-Date(master): Thu May 26 06:21:10 CEST 2016 on sn-devel-144