Add support for building without Frr #1670

For smaller switch-only deployments there's been a demand for building without Frr, which brings in a lot of dependencies like Bash, which in turn brings in other dependencies.

The minimal defconfigs should be the battle ground for building without Frr, where /bin/bash then becomes /bin/ash -- all deps from bash and frr et al are discarded for a truly minimal build. Not unlike how with or without container support is built today.

The netd daemon plays a key role here, relaying static routes to staticd (frr) or directly to the kernel, and it's actually sort of prepared to shoulder the mantle.