CVE-2016-2111: s3:rpc_server/netlogon: check NTLMv2_RESPONSE values for SEC_CHAN_WKSTA

This prevents spoofing like Microsoft's CVE-2015-0005.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11749

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Günther Deschner <gd@samba.org>
