This patch adds a host route to an interface address (that is assigned
to a non loopback/ppp link type) through the loopback interface. Prior
to the new L2/L3 rewrite, this host route was explicitly created when
processing the IPv6 address assignment. This loopback host route is
deleted when that IPv6 address is removed from the interface.

Reviewed by: bz, gnn
Approved by: re