CVE-2016-2111: libcli/auth: add NTLMv2_RESPONSE_verify_netlogon_creds() helper function

This is the function that 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>
