Stop sending messages on legacy substream altogether (#6975)

* Stop sending messages on legacy substream altogether

* Ensure that handshake is sent back even in case of back-pressure

* Update client/network/src/protocol/generic_proto/handler/group.rs

Co-authored-by: Max Inden <mail@max-inden.de>

* Also process OpenRequest and Closed

* Also process OpenRequest and Closed

* Fix bad merge

* God I'm so lost with all these merges

* Immediately return Closed

* Add warning for sending on non-registered protocol

* Register GrandPa protocol in tests

* Update client/network/src/protocol/generic_proto/handler/group.rs

Co-authored-by: Max Inden <mail@max-inden.de>

Co-authored-by: Max Inden <mail@max-inden.de>

substrate/client/finality-grandpa/src/tests.rs

@@ -23,7 +23,7 @@ use assert_matches::assert_matches;
 use environment::HasVoted;
 use sc_network_test::{
 	Block, BlockImportAdapter, Hash, PassThroughVerifier, Peer, PeersClient, PeersFullClient,
-	TestClient, TestNetFactory,
+	TestClient, TestNetFactory, FullPeerConfig,
 };
 use sc_network::config::{ProtocolConfig, BoxFinalityProofRequestBuilder};
 use parking_lot::Mutex;
@@ -94,6 +94,15 @@ impl TestNetFactory for GrandpaTestNet {
 		ProtocolConfig::default()
 	}
 
+	fn add_full_peer(&mut self) {
+		self.add_full_peer_with_config(FullPeerConfig {
+			notifications_protocols: vec![
+				(communication::GRANDPA_ENGINE_ID, communication::GRANDPA_PROTOCOL_NAME.into())
+			],
+			..Default::default()
+		})
+	}
+
 	fn make_verifier(
 		&self,
 		_client: PeersClient,