[PATCH v3] Babel: Replace internal route selection by bird's nest

[nick]

Hi BIRD-Community,
I wanted to bring this patch back into focus. We run a non-commercial 
WISP-network with Babel and switched to BIRD due to limitations in 
babeld. While BIRD works great, we urgently need this patch for better 
route filtering flexibility.

It’d be great to see this upstream to save projects from maintaining 
downstream versions.

Thanks,
Nick