luci-app-strongswan-swanctl: rename lifetime to life_time in child

Rename the 'lifetime' option to 'life_time' in the uci section type
'child' to follow the naming convention and improve consistency with
'swanctl.conf' terminology.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>

applications/luci-app-strongswan-swanctl/htdocs/luci-static/resources/view/strongswan-swanctl/swanctl.js

@@ -383,7 +383,7 @@ return view.extend({
 		o.rmempty = true;
 		o.modalonly = true;
 
-		o = s.taboption('advanced', form.Value, 'lifetime', _('Life Time'),
+		o = s.taboption('advanced', form.Value, 'life_time', _('Life Time'),
 			_('Maximum time before the CHILD_SA gets closed, as a hard limit.')
 		);
 		o.validate = validateTimeFormat;