Actually connect to new validators at session boundary. (#3055)

* Actually connect to new validators at session boundary.

* Add tracing.

node/network/gossip-support/src/lib.rs

@@ -102,6 +102,11 @@ async fn determine_relevant_authorities(
 	relay_parent: Hash,
 ) -> Result<Vec<AuthorityDiscoveryId>, util::Error> {
 	let authorities = util::request_authorities(relay_parent, ctx.sender()).await.await??;
+	tracing::debug!(
+		target: LOG_TARGET,
+		authority_count = ?authorities.len(),
+		"Determined relevant authorities"
+	);
 	Ok(authorities)
 }
 
@@ -152,7 +157,7 @@ impl State {
 		for leaf in leaves {
 			let current_index = util::request_session_index_for_child(leaf, ctx.sender()).await.await??;
 			let maybe_new_session = match self.last_session_index {
-				Some(i) if i <= current_index => None,
+				Some(i) if i >= current_index => None,
 				_ => Some((current_index, leaf)),
 			};