luci-mod-network: routes.js: make interface setting optional

Fixes: openwrt#7260
Ref: https://git.openwrt.org/5c2e5d5ea4e0dd9a0ed66154d818b96bf81664f4
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

modules/luci-mod-network/htdocs/luci-static/resources/view/network/routes.js

@@ -41,7 +41,7 @@ return view.extend({
 			o = s.taboption('general', widgets.NetworkSelect, 'interface', _('Interface'), _('Specifies the logical interface name of the parent (or master) interface this route belongs to'));
 			o.loopback = true;
 			o.nocreate = true;
-			o.rmempty = false;
+			o.rmempty = true;
 
 			o = s.taboption('general', form.ListValue, 'type', _('Route type'), _('Specifies the route type to be created'));
 			o.modalonly = true;