ddns-scripts: only start via hotplug not via boot

Hotplug script will start service for each interface.
To prevent duplicates and in general must not start on boot.

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>
ddns-scripts: start via hotplug only if enabled

To be consistent with other services only start via hotplug if enabled.
Now full functionality of /etc/init.d/ddns enable/disable start/stop

Optimization: Include script only if needed

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>
ddns-scripts: new service "spdns.de"

Service provided by Securepoint GmbH, 21335 Lüneburg, Germany
Info at http://www.spdns.de

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>
Merge pull request #134 from chris5560/master

ddns-scripts: minor updates