libnet_join: fix "net rpc oldjoin"

libnet_join: fix "net rpc oldjoin"

We need to open the ncacn_np (smb) transport connection with
anonymous credentials.

In order to do netr_ServerPasswordSet*() we need to
establish a 2nd netlogon connection using dcerpc schannel
authentication.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13149

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
(similar to commit d27f38d35bf111a5c0a898a5ef8b7dd0b320da0d)

Autobuild-User(v4-6-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-6-test): Wed Nov 29 12:59:34 CET 2017 on sn-devel-144