CVE-2016-2110: auth/ntlmssp: split allow_lm_response from allow_lm_key

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11644

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