Prevent remote submix devices from disconnecting before test finish

On low-end platforms, when AudioTrack does not
write data to audioflinger, that may be buffer timeout
due to not receiving data, flinger will remove the track, causing
policy to disconnect remote-submix device.
However, the test has not yet ended, causing the test failed.

Bug: 370403135
Test: atest VirtualAudioPermissionTest#audioInjection_virtualDeviceWithManualAudioPolicy_permissionGrantedOnlyOnDefaultDevice

Change-Id: I52e2785ee5a94f43f77d860b5d2bd5de9dc3fbb6