CVE-2016-2111: s4:libcli: don't allow the LANMAN2 session setup without "client lanman auth = yes"

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

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
