Gossipsub scoring (#1668)

## Issue Addressed

#1606 

## Proposed Changes

Uses dynamic gossipsub scoring parameters depending on the number of active validators as specified in https://gist.github.com/blacktemplar/5c1862cb3f0e32a1a7fb0b25e79e6e2c.

## Additional Info

Although the parameters got tested on Medalla, extensive testing using simulations on larger networks is still to be done and we expect that we need to change the parameters, although this might only affect constants within the dynamic parameter framework.

beacon_node/eth2_libp2p/src/service.rs

@@ -23,7 +23,7 @@ use std::io::prelude::*;
 use std::pin::Pin;
 use std::sync::Arc;
 use std::time::Duration;
-use types::{EnrForkId, EthSpec};
+use types::{ChainSpec, EnrForkId, EthSpec};
 
 pub const NETWORK_KEY_FILENAME: &str = "key";
 /// The maximum simultaneous libp2p connections per peer.
@@ -62,6 +62,7 @@ impl<TSpec: EthSpec> Service<TSpec> {
         config: &NetworkConfig,
         enr_fork_id: EnrForkId,
         log: &slog::Logger,
+        chain_spec: &ChainSpec,
     ) -> error::Result<(Arc<NetworkGlobals<TSpec>>, Self)> {
         let log = log.new(o!("service"=> "libp2p"));
         trace!(log, "Libp2p Service starting");
@@ -104,8 +105,14 @@ impl<TSpec: EthSpec> Service<TSpec> {
             let transport = build_transport(local_keypair.clone())
                 .map_err(|e| format!("Failed to build transport: {:?}", e))?;
             // Lighthouse network behaviour
-            let behaviour =
-                Behaviour::new(&local_keypair, config, network_globals.clone(), &log).await?;
+            let behaviour = Behaviour::new(
+                &local_keypair,
+                config,
+                network_globals.clone(),
+                &log,
+                chain_spec,
+            )
+            .await?;
 
             // use the executor for libp2p
             struct Executor(task_executor::TaskExecutor);