BEEFY: optimize voter event loop for fewer 'active' wakeups (#12760)

* client/beefy: remove high-freq network events from main loop

Network events are many and very frequent, remove the net-event-stream
from the main voter loop and drastically reduce BEEFY voter task
'wakeups'.

Instead have the `GossipValidator` track known peers as it already
has callbacks for that coming from `GossipEngine`.

Signed-off-by: acatangiu <adrian@parity.io>

substrate/client/beefy/src/lib.rs

@@ -241,11 +241,12 @@ where
 		None,
 	);
 
+	// The `GossipValidator` adds and removes known peers based on valid votes and network events.
 	let on_demand_justifications = OnDemandJustificationsEngine::new(
 		network.clone(),
 		runtime.clone(),
 		justifications_protocol_name,
-		known_peers.clone(),
+		known_peers,
 	);
 
 	let metrics =
@@ -286,7 +287,6 @@ where
 		payload_provider,
 		network,
 		key_store: key_store.into(),
-		known_peers,
 		gossip_engine,
 		gossip_validator,
 		on_demand_justifications,