improved gossip topology (#3270)

* gossip-support: gossip topology

* some fixes

* handle view update for newly added gossip peers

* fix neighbors calculation

* fix test

* resolve TODOs

* typo

* guide updates

* spaces in the guide

* sneaky spaces

* hash randomness

* address some review nits

* use unbounded in bridge for subsystem msg

polkadot/node/network/collator-protocol/src/collator_side/mod.rs

@@ -795,6 +795,9 @@ async fn handle_network_msg(
 		PeerMessage(remote, msg) => {
 			handle_incoming_peer_message(ctx, runtime, state, remote, msg).await?;
 		}
+		NewGossipTopology(..) => {
+			// impossibru!
+		}
 	}
 
 	Ok(())

polkadot/node/network/collator-protocol/src/validator_side/mod.rs

@@ -899,6 +899,9 @@ where
 			state.peer_data.remove(&peer_id);
 			state.metrics.note_collator_peer_count(state.peer_data.len());
 		},
+		NewGossipTopology(..) => {
+			// impossibru!
+		}
 		PeerViewChange(peer_id, view) => {
 			handle_peer_view_change(state, peer_id, view).await?;
 		},