swarm/network: Complete healthy parameters

[nolash]

Currently a node can be healthy by having neighbours only.

AFAIK, the current idea of healthiness is:

• you know of and are connected to all neighbors
• if depth value is greater than 0, you should know of and be connected to at least one peer in each bin shallower than depth.

Previously we had a method full which I believe was part of making sure of this. It can be found eg. in 362e2ba

For the abandoned work on the kademlia cleanup I introduced a notion "potent" which was supposed to be this exact check. It also has unit tests. The branch in question is here: #1108

Hopefully the task is not much more than superimposing this work on top of the current head, and making sure that the simulation tests have the right expectations.

[holisticode]

After a call with @zelig it became clear that the work for this ticket is not correctly described.

According to @zelig we need to refactor the notion of Saturated such that the PeerPot is passed the ideal version of the kademlia, and then compare with the real one - that will determine saturation.

The rows below the depth there is a choice of multiple peers to fill the bins, so we compare connections with MinBinSize; the nearest neighbours will need exact match

[holisticode]

Closed by ethereum/go-ethereum#19071