dsdb/netlogon: Indicate DC functional level support in samlogon response

dsdb/netlogon: Indicate DC functional level support in samlogon response

The DS_SERVER_DS_8 flag is necessary for Windows to detect FAST support.

Note for know we only ever have DS_DOMAIN_FUNCTION_2008_R2 (4) in the
msDS-Behavior-Version attribute of our own NTDSA object. So
for now this is only for manual testing. In future we most likely
want to extend 'samba-tool domain level' to raise the dc level
manually or let 'samba' autoupgrade the value.

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Signed-off-by: Stefan Metzmacher <metze@samba.org>