Fix SMB3.1.1 guest authentication to Samba

commit 23586b66d84ba3184b8820277f3fc42761640f87 upstream.

Samba rejects SMB3.1.1 dialect (vers=3.1.1) negotiate requests from
the kernel client due to the two byte pad at the end of the negotiate
contexts.

Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>