feeds.conf.default: restore the old package feed temporarily

As explained here:
https://forum.openwrt.org/viewtopic.php?id=51078



allow both the old and the new packages feed to co-exist for a grace
period of 3 weeks, allowing maintainers to move packages progressively.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

SVN-Revision: 41149