request for missed ifupdown ipv6 patch

[Natanael Copa]

This patch seems to have been forgotten and is needed for ipv6 to work properly:
http://lists.busybox.net/pipermail/busybox/2012-August/078297.html

Could it please be added thanks?

I am getting tired of rebasing it every release.

-nc

PS. have you considered using patchwork? It helped alpine linux alot
when patches started to fall between the cracks. Might be
http://patchwork.ozlabs.org/ can host it for you too.