Clean up sc-network (#9761)

* Clean up sc-network

- Avoid using clone() for the Copy type `PeerId`.
- Use `find_map` for `filter_map` and `next`.
- Use `Self`.

* More on Copy types

* Cargo +nightly fmt --all

* More ..

* fmt

* Revert vec![default_notif_handshake_message]

substrate/client/network/src/protocol/event.rs

@@ -117,6 +117,6 @@ pub enum ObservedRole {
 impl ObservedRole {
 	/// Returns `true` for `ObservedRole::Light`.
 	pub fn is_light(&self) -> bool {
-		matches!(self, ObservedRole::Light)
+		matches!(self, Self::Light)
 	}
 }