discv5: collect more eclipse attack countermeasures

The eclipse attack texts deletes the previous information and references to the "Bound-LogIDforPhyIDSrc" in this paper https://engineering.purdue.edu/~isl/TR-EE-07-13.pdf

Instead, the text now makes a general suggestion to limit /24 subnet IPs by bucket and table.

Both approaches have their limitations. In the former case, it is difficult to establish what the correct weighting of per-learned-from-source should be, and with the latter I feel a determined attacker may still be able to take advantage of delays in the node verification schedule to propagate junk around a target and with self-propagation.

I would prefer if the implementation recommendation was more agnostic about how these attacks should be mitigated, while proposing multiple strategies and referring to the papers.