swaybar: only subscribe to required events

This adds barconfig_update to the list of subscribed events, as well as
checking when the other events need to be subscribed to.

swaybar/ipc.c

@@ -356,8 +356,12 @@ bool ipc_initialize(struct swaybar *bar) {
 	free(res);
 	ipc_get_outputs(bar);
 
-	const char *subscribe = "[ \"workspace\", \"mode\" ]";
-	len = strlen(subscribe);
+	struct swaybar_config *config = bar->config;
+	char subscribe[128]; // suitably large buffer
+	len = snprintf(subscribe, 128,
+			"[ \"barconfig_update\" %s %s ]",
+			config->binding_mode_indicator ? ", \"mode\"" : "",
+			config->workspace_buttons ? ", \"workspace\"" : "");
 	free(ipc_single_command(bar->ipc_event_socketfd,
 			IPC_SUBSCRIBE, subscribe, &len));
 	return true;