test_vendor: Stop watching before closing the FD

Test: net_test_bluetooth BluetoothTest.AdapterRepeatedEnableDisable
Change-Id: I72f5c9105b535ad5a5c41bc15dc9a3ad5f4e023f

system/vendor_libs/test_vendor_lib/src/vendor_manager.cc

@@ -110,7 +110,10 @@ void VendorManager::SetUpTestChannel(int port) {
   });
 }
 
-void VendorManager::CloseHciFd() { transport_.CloseHciFd(); }
+void VendorManager::CloseHciFd() {
+  async_manager_.StopWatchingFileDescriptor(transport_.GetHciFd());
+  transport_.CloseHciFd();
+}
 
 int VendorManager::GetHciFd() const { return transport_.GetHciFd(); }