Bluetooth: Export AsyncFdWatcher for reuse

Test: Bluetooth starts/stops
Change-Id: I1dcd8684fd150b5eb27c75e5d7803070009e0bf5
diff --git a/bluetooth/1.0/default/vendor_interface.h b/bluetooth/1.0/default/vendor_interface.h
index ce5769c..98357f5 100644
--- a/bluetooth/1.0/default/vendor_interface.h
+++ b/bluetooth/1.0/default/vendor_interface.h
@@ -59,7 +59,7 @@
 
   void *lib_handle_;
   bt_vendor_interface_t *lib_interface_;
-  AsyncFdWatcher fd_watcher_;
+  async::AsyncFdWatcher fd_watcher_;
   int uart_fd_;
   PacketReadCallback packet_read_cb_;
   InitializeCompleteCallback initialize_complete_cb_;