Update filter.tpl

fixed template in order to allow save settings, without the "filter_" part, the model_setting_settings->editsettings dont work because the check on line 23
if (substr($key, 0, strlen($code)) == $code) {

I don't know if this was intentionally because filter module still need attention?
Merge pull request #2357 from CoverUp/patch-1

Update filter.tpl