Fix clippy warnings (#1385)

## Issue Addressed

NA

## Proposed Changes

Fixes most clippy warnings and ignores the rest of them, see issue #1388.

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

@@ -100,6 +100,7 @@ impl<TSpec: EthSpec> ProtocolsHandler for BehaviourHandler<TSpec> {
         KeepAlive::Yes
     }
 
+    #[allow(clippy::type_complexity)]
     fn poll(
         &mut self,
         cx: &mut Context,