Declare state directory in smb.conf

The smb.conf generated by the userspace networking does not include a state directory
directive. Samba therefore falls back to the default value. Since the user generally
does not have write access to this path, smbd immediately crashes.

The "state directory" option was added in Samba 3.4.0 (commit
http://gitweb.samba.org/?p=samba.git;a=commit;h=7b02e05eb64f3ffd7aa1cf027d10a7343c0da757).

This patch adds the missing option.

Signed-off-by: Nikolaus Rath <Nikolaus@rath.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
