Updates OpenWRT package repository URL.

Now that OpenWRT 14.07 is final and used in Gluon, we should update the
URL to the package repo from 14.07-rc3 to 14.07 as well. Moreover, the old
IPv6-capable mirroring host (http://openwrt.draic.info/) does not provide the
packages any longer, hence http://bo.mirror.garr.it/ got chosen to be the new
mirror.

site.conf

@@ -20,7 +20,7 @@
 	ntp_servers = {'ntp.services.ffpb'},
 
         -- OpenWRT Package Repository (IPv6 capable)
-	opkg_repo = 'http://openwrt.draic.info/barrier_breaker/14.07-rc3/%S/packages',
+	opkg_repo = 'http://bo.mirror.garr.it/pub/1/openwrt/barrier_breaker/14.07/%S/packages/',
 
 	-- regulatory domain of your wifi
 	regdom = 'DE',