luci-mod-network: use firewall.getZoneColorStyle() in interface view

Use the new `firewall.getZoneColorStyle()` helper to apply background
zone color styles to the interface boxes.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 849772df96)

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

@@ -1187,7 +1187,7 @@ return view.extend({
 			var node = E('div', { 'class': 'ifacebox' }, [
 				E('div', {
 					'class': 'ifacebox-head',
-					'style': 'background-color:%s'.format(zone ? zone.getColor() : '#EEEEEE'),
+					'style': firewall.getZoneColorStyle(zone),
 					'title': zone ? _('Part of zone %q').format(zone.getName()) : _('No zone assigned')
 				}, E('strong', net.getName().toUpperCase())),
 				E('div', {