Dandelion with no outbound connections will freeze.
We should provide a way for the `outbound_peer_discover` to tell us there are currently not enough peers.

relevant code: 

https://github.com/Cuprate/cuprate/blob/b76042a4e4f364aa2c3b53235f30382ac632d2e8/p2p/dandelion/src/router.rs#L164-L179