Misc Peer sync info adjustments (#1896)

## Issue Addressed
#1856 

## Proposed Changes
- For clarity, the router's processor now only decides if a peer is compatible and it disconnects it or sends it to sync accordingly. No logic here regarding how useful is the peer. 
- Update peer_sync_info's rules
- Add an `IrrelevantPeer` sync status to account for incompatible peers (maybe this should be "IncompatiblePeer" now that I think about it?) this state is update upon receiving an internal goodbye in the peer manager
- Misc code cleanups
- Reduce the need to create `StatusMessage`s (and thus, `Arc` accesses )
- Add missing calls to update the global sync state

The overall effect should be:
- More peers recognized as Behind, and less as Unknown
- Peers identified as incompatible

beacon_node/network/src/sync/network_context.rs

@@ -63,7 +63,7 @@ impl<T: EthSpec> SyncNetworkContext<T> {
         chain: Arc<BeaconChain<U>>,
         peers: impl Iterator<Item = PeerId>,
     ) {
-        if let Some(status_message) = status_message(&chain) {
+        if let Ok(status_message) = status_message(&chain) {
             for peer_id in peers {
                 debug!(
                     self.log,