s3:libsmb: use 16 zero bytes as channel binding checksum in the gssapi checksum ...

s3:libsmb: use 16 zero bytes as channel binding checksum in the gssapi checksum (bug #7883)

This fixes SMB session setups with kerberos against some closed
source SMB servers.

The new behavior matches heimdal and mit.

metze

Autobuild-User: Stefan Metzmacher <metze@samba.org>
Autobuild-Date: Thu Dec 23 09:38:43 CET 2010 on sn-devel-104
(cherry picked from commit e9dddc55e324c62973e6a561477b532cf9ed79af)
(cherry picked from commit 3356192af5d36fbe986c4728162d10fe883ba2fd)
(cherry picked from commit 3d9dd75e811eb251002b7c1b958f58790a089086)