Add failure reply on IPC_SYNC

Since it was decided that sway will not support IPC_SYNC, just return
`{'success': false}` as a reply

include/ipc.h

@@ -16,6 +16,7 @@ enum ipc_command_type {
 	IPC_GET_BINDING_MODES = 8,
 	IPC_GET_CONFIG = 9,
 	IPC_SEND_TICK = 10,
+	IPC_SYNC = 11,
 
 	// sway-specific command types
 	IPC_GET_INPUTS = 100,

sway/ipc-server.c

@@ -836,6 +836,14 @@ void ipc_client_handle_command(struct ipc_client *client) {
 		goto exit_cleanup;
     }
 
+	case IPC_SYNC:
+	{
+		// It was decided sway will not support this, just return success:false
+		const char msg[] = "{\"success\": false}";
+		ipc_send_reply(client, msg, strlen(msg));
+		goto exit_cleanup;
+	}
+
 	default:
 		wlr_log(WLR_INFO, "Unknown IPC command type %i", client->current_command);
 		goto exit_cleanup;