site.conf: load packages from firmware.ffh.zone

Due to our decentralized build structure workspaces are not retained
as reliably as they once were. This is not problematic for nightly
builds as they heal within a day, but for releases running over longer
periods.

(cherry picked from commit 150f503)

site.conf

@@ -8,7 +8,7 @@
 	opkg = {
 		openwrt = 'http://downloads.openwrt.org/releases/packages-%v/%A',
 		extra = {
-			modules = 'http://build.ffh.zone/job/gluon-beta/ws/beta/packages/gluon-%GS-%GR/%S',
+			modules = 'http://firmware.ffh.zone/packages/gluon-%GS-%GR/%S',
 		},
 	},