This also fixes a bug in sending ihu intervals.

I'm not sure what the scope attribute of routes is supposed to mean.
Both ifconfig and ip route appear to add IPv4 routes to directly
connected networks with link scope, and we definitely don't want to
prevent exporting such routes.
For what it's worth, that's also what Quagga does.

It's an enum, not a #define, so the #ifdef RTA_TABLE never triggered.

This is needed when there is no route to the gateway.