Disconnect peers (#1484)

## Issue Addressed

Peers that connected after the peer limit may remain connected in some circumstances. 

This ensures peers not in the peer manager's list get disconnected. Further logging is also added to track this behaviour.

beacon_node/eth2_libp2p/src/behaviour/handler/delegate.rs

@@ -49,7 +49,7 @@ impl<TSpec: EthSpec> DelegatingHandler<TSpec> {
     }
 
     /// Gives access to identify's handler.
-    pub fn identify(&self) -> &IdentifyHandler {
+    pub fn _identify(&self) -> &IdentifyHandler {
         &self.identify_handler
     }
 }