Altair networking (#2300)

## Issue Addressed

Resolves #2278 

## Proposed Changes

Implements the networking components for the Altair hard fork https://github.com/ethereum/eth2.0-specs/blob/dev/specs/altair/p2p-interface.md

## Additional Info

This PR acts as the base branch for networking changes and tracks https://github.com/sigp/lighthouse/pull/2279 . Changes to gossip, rpc and discovery can be separate PRs to be merged here for ease of review.

Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/eth2_libp2p/tests/common/mod.rs

@@ -7,14 +7,20 @@ use eth2_libp2p::{Libp2pEvent, NetworkConfig};
 use libp2p::gossipsub::GossipsubConfigBuilder;
 use slog::{debug, error, o, Drain};
 use std::net::{TcpListener, UdpSocket};
+use std::sync::Arc;
 use std::sync::Weak;
 use std::time::Duration;
 use tokio::runtime::Runtime;
-use types::{ChainSpec, EnrForkId, MinimalEthSpec};
+use types::{ChainSpec, EnrForkId, ForkContext, Hash256, MinimalEthSpec};
 
 type E = MinimalEthSpec;
 use tempfile::Builder as TempBuilder;
 
+/// Returns a dummy fork context
+fn fork_context() -> ForkContext {
+    ForkContext::new::<E>(types::Slot::new(0), Hash256::zero(), &ChainSpec::minimal())
+}
+
 pub struct Libp2pInstance(LibP2PService<E>, exit_future::Signal);
 
 impl std::ops::Deref for Libp2pInstance {
@@ -109,12 +115,14 @@ pub async fn build_libp2p_instance(
     let (signal, exit) = exit_future::signal();
     let (shutdown_tx, _) = futures::channel::mpsc::channel(1);
     let executor = task_executor::TaskExecutor::new(rt, exit, log.clone(), shutdown_tx);
+    let fork_context = Arc::new(fork_context());
     Libp2pInstance(
         LibP2PService::new(
             executor,
             &config,
             EnrForkId::default(),
             &log,
+            fork_context,
             &ChainSpec::minimal(),
         )
         .await