Downgrade libp2p (#1817)

## Description

This downgrades the recent libp2p upgrade. 

There were issues with the RPC which prevented syncing of the chain and this upgrade needs to be further investigated.

beacon_node/network/src/nat.rs

@@ -4,7 +4,7 @@
 //! - UPnP
 
 use crate::{NetworkConfig, NetworkMessage};
-use if_addrs::get_if_addrs;
+use get_if_addrs::get_if_addrs;
 use slog::{debug, info, warn};
 use std::net::{IpAddr, SocketAddr, SocketAddrV4};
 use tokio::sync::mpsc;

beacon_node/network/src/service.rs

@@ -428,6 +428,7 @@ fn spawn_service<T: BeaconChainTypes>(
                                 id,
                                 source,
                                 message,
+                                ..
                             } => {
                                 // Update prometheus metrics.
                                 expose_receive_metrics(&message);