p2p/discover, p2p/enode: rework endpoint proof handling, packet logging (#18963)

This change resolves multiple issues around handling of endpoint proofs.
The proof is now done separately for each IP and completing the proof
requires a matching ping hash.

Also remove waitping because it's equivalent to sleep. waitping was
slightly more efficient, but that may cause issues with findnode if
packets are reordered and the remote end sees findnode before pong.

Logging of received packets was hitherto done after handling the packet,
which meant that sent replies were logged before the packet that
generated them. This change splits up packet handling into 'preverify'
and 'handle'. The error from 'preverify' is logged, but 'handle' happens
after the message is logged. This fixes the order. Packet logs now
contain the node ID.

p2p/discover/node.go

@@ -33,7 +33,8 @@ import (
 // The fields of Node may not be modified.
 type node struct {
 	enode.Node
-	addedAt time.Time // time when the node was added to the table
+	addedAt        time.Time // time when the node was added to the table
+	livenessChecks uint      // how often liveness was checked
 }
 
 type encPubkey [64]byte