Combine default values used at initialization in a trait (#6857)

This moves default values used in the Substrate code base when
initializing a service into a common trait. Currently this trait only
contains listen ports, but this could be extended in the future.
Essentially this will make overriding these values much easier for
Cumulus, where we have 2 nodes running in one binary.

substrate/client/cli/src/params/network_params.rs

@@ -114,8 +114,9 @@ impl NetworkParams {
 		client_id: &str,
 		node_name: &str,
 		node_key: NodeKeyConfig,
+		default_listen_port: u16,
 	) -> NetworkConfiguration {
-		let port = self.port.unwrap_or(30333);
+		let port = self.port.unwrap_or(default_listen_port);
 
 		let listen_addresses = if self.listen_addr.is_empty() {
 			vec![