Add IPv6 Support

[areynold]

The auto-generation of IPv4 addresses on both the mesh and client networks is a kludge, which has the potential for collision on a large enough network. The ideal would be to use IPv6 address autoconfiguration on the mesh backhaul by default, and have the option for IPv6 connectivity on all of the client networks.

• Add necessary options into /lib/network/mesh.sh to bypass the generation of the IPv4 addresses for the meshif and apif interfaces, based on an option found in the /etc/config/network for a given interface (and maybe defaults from /etc/config/mesh if appropriate).
• Add function into /etc/hotplug.d/services/20-olsrd that generates the appropriate Interface and HNA6 stanzas in /etc/config/olsrd if using IPv6 on an interface.
• Change default olsrd config to activate NIIT

(Was Issue 89 on code.commotionwireless.net)

[glamrock]

As of Attitude Adjustment 12.09.1, there's native support for IPv6 with package ipv6-support. Would it perhaps be better to upgrade OpenWrt entirely?