Decouple SubscriptionController from Controller

Remove the reliance a reference to the Controller to get the link that a
subscription is tied to by explicitly handling the SubscriptionRequest
and passing the link to the SubscriptionController.

packages/controller/src/BaseConnection.ts

@@ -34,6 +34,7 @@ export default class BaseConnection extends lib.Link {
 		this.handle(lib.ModPackGetDefaultRequest, this.handleModPackGetDefaultRequest.bind(this));
 		this.handle(lib.ModDownloadRequest, this.handleModDownloadRequest.bind(this));
 
+		this.handle(lib.SubscriptionRequest, this.handleSubscriptionRequest.bind(this));
 		this.connector.on("close", () => {
 			this._controller.subscriptions.unsubscribe(this);
 		});
@@ -102,4 +103,8 @@ export default class BaseConnection extends lib.Link {
 
 		return stream.id;
 	}
+
+	async handleSubscriptionRequest(request: lib.SubscriptionRequest, src: lib.Address, dst: lib.Address) {
+		return await this._controller.subscriptions.handleRequest(this, request, src, dst);
+	}
 }