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>

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>

Signed-off-by: Nikos Mavrogiannopoulos <nmav@gnutls.org>