Don't create routing table entry for unsafe_routes that directly map to locally connected subnets.

For example, say your office is 192.168.3.0/24, and you have an unsafe_route on your laptop to use the router at your office as a gateway to this subnet. When you are away from the office, all is well. When you go to your office, your traffic will needlessly go to the router, over nebula, to reach devices on the local network. This is probably not what most people want to happen.