config directory incorrect for the samba plugin

Since 1.0.5, all plugins which need it have a config directory with several classes into it.

Normally for all plugins, the structure of the config tree into the sources is config/<plugin_name>/.

But for the samba plugin, files are directly into the config directory which is non compliant with the others plugins. It should be changed.

(from redmine: issue id 2377, created on 2013-05-08, closed on 2013-05-09)

Fixes: #2377 config directory incorrect for the samba plugin