The existing event based method of watching for has_network has a flaw.
The incoming route_change events from probert do not distinguish routes
on the same interface but a different metric, so if 2 routes on one
interface appear, we only get one event. Then if one of those routes is
removed, we will inappropriately remove this route from the
default_routes list.
Aside from the code watching the event stream, the set of default routes
is an elaborate boolean value.
Simplify the code by passing around a boolean, and when we get a
route_change event, use that to go looking again at the list of default
routes.
LP: #2004659
Dan Bungert