Check fork_id before attempting to initiate an RLPx connection

[ElFantasma]

Now that we are requesting ENRs from peers, we can filter valid contacts to initiate RLPx connections on lookup.

We should validate fork_id field when receiving ENRResponses and use that information to filter on get_contact_for_lookup

Geth seems to be doing the same: https://github.com/ethereum/go-ethereum/blob/d3679c2f2e9d7f6d354375bfad0165016e6d059c/eth/protocols/eth/discovery.go#L71-L80

Related: #5423