Integrate litep2p into Polkadot SDK (#2944)

[litep2p](https://github.com/altonen/litep2p) is a libp2p-compatible P2P
networking library. It supports all of the features of `rust-libp2p`
that are currently being utilized by Polkadot SDK.

Compared to `rust-libp2p`, `litep2p` has a quite different architecture
which is why the new `litep2p` network backend is only able to use a
little of the existing code in `sc-network`. The design has been mainly
influenced by how we'd wish to structure our networking-related code in
Polkadot SDK: independent higher-levels protocols directly communicating
with the network over links that support bidirectional backpressure. A
good example would be `NotificationHandle`/`RequestResponseHandle`
abstractions which allow, e.g., `SyncingEngine` to directly communicate
with peers to announce/request blocks.

I've tried running `polkadot --network-backend litep2p` with a few
different peer configurations and there is a noticeable reduction in
networking CPU usage. For high load (`--out-peers 200`), networking CPU
usage goes down from ~110% to ~30% (80 pp) and for normal load
(`--out-peers 40`), the usage goes down from ~55% to ~18% (37 pp).

These should not be taken as final numbers because:

a) there are still some low-hanging optimization fruits, such as
enabling [receive window
auto-tuning](https://github.com/libp2p/rust-yamux/pull/176), integrating
`Peerset` more closely with `litep2p` or improving memory usage of the
WebSocket transport
b) fixing bugs/instabilities that incorrectly cause `litep2p` to do less
work will increase the networking CPU usage
c) verification in a more diverse set of tests/conditions is needed

Nevertheless, these numbers should give an early estimate for CPU usage
of the new networking backend.

This PR consists of three separate changes:
* introduce a generic `PeerId` (wrapper around `Multihash`) so that we
don't have use `NetworkService::PeerId` in every part of the code that
uses a `PeerId`
* introduce `NetworkBackend` trait, implement it for the libp2p network
stack and make Polkadot SDK generic over `NetworkBackend`
  * implement `NetworkBackend` for litep2p

The new library should be considered experimental which is why
`rust-libp2p` will remain as the default option for the time being. This
PR currently depends on the master branch of `litep2p` but I'll cut a
new release for the library once all review comments have been
addresses.

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Dmitry Markin <dmitry@markin.tech>
Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>
Co-authored-by: Alexandru Vasile <alexandru.vasile@parity.io>

templates/parachain/node/src/service.rs

@@ -27,7 +27,7 @@ use frame_benchmarking_cli::SUBSTRATE_REFERENCE_HARDWARE;
 use sc_client_api::Backend;
 use sc_consensus::ImportQueue;
 use sc_executor::{HeapAllocStrategy, WasmExecutor, DEFAULT_HEAP_ALLOC_STRATEGY};
-use sc_network::NetworkBlock;
+use sc_network::{NetworkBackend, NetworkBlock};
 use sc_network_sync::SyncingService;
 use sc_service::{Configuration, PartialComponents, TFullBackend, TFullClient, TaskManager};
 use sc_telemetry::{Telemetry, TelemetryHandle, TelemetryWorker, TelemetryWorkerHandle};
@@ -131,7 +131,7 @@ pub fn new_partial(config: &Configuration) -> Result<Service, sc_service::Error>
 ///
 /// This is the actual implementation that is abstract over the executor and the runtime api.
 #[sc_tracing::logging::prefix_logs_with("Parachain")]
-async fn start_node_impl(
+async fn start_node_impl<N: NetworkBackend<Block, Hash>>(
 	parachain_config: Configuration,
 	polkadot_config: Configuration,
 	collator_options: CollatorOptions,
@@ -142,7 +142,8 @@ async fn start_node_impl(
 
 	let params = new_partial(&parachain_config)?;
 	let (block_import, mut telemetry, telemetry_worker_handle) = params.other;
-	let net_config = sc_network::config::FullNetworkConfiguration::new(&parachain_config.network);
+	let net_config =
+		sc_network::config::FullNetworkConfiguration::<_, _, N>::new(&parachain_config.network);
 
 	let client = params.client.clone();
 	let backend = params.backend.clone();
@@ -191,7 +192,7 @@ async fn start_node_impl(
 				transaction_pool: Some(OffchainTransactionPoolFactory::new(
 					transaction_pool.clone(),
 				)),
-				network_provider: network.clone(),
+				network_provider: Arc::new(network.clone()),
 				is_validator: parachain_config.role.is_authority(),
 				enable_http_requests: false,
 				custom_extensions: move |_| vec![],
@@ -416,5 +417,24 @@ pub async fn start_parachain_node(
 	para_id: ParaId,
 	hwbench: Option<sc_sysinfo::HwBench>,
 ) -> sc_service::error::Result<(TaskManager, Arc<ParachainClient>)> {
-	start_node_impl(parachain_config, polkadot_config, collator_options, para_id, hwbench).await
+	match polkadot_config.network.network_backend {
+		sc_network::config::NetworkBackendType::Libp2p =>
+			start_node_impl::<sc_network::NetworkWorker<_, _>>(
+				parachain_config,
+				polkadot_config,
+				collator_options,
+				para_id,
+				hwbench,
+			)
+			.await,
+		sc_network::config::NetworkBackendType::Litep2p =>
+			start_node_impl::<sc_network::Litep2pNetworkBackend>(
+				parachain_config,
+				polkadot_config,
+				collator_options,
+				para_id,
+				hwbench,
+			)
+			.await,
+	}
 }