If we have virtual_oss running, this devd notification will make sure to
automatically transfer sound to the new default unit, while also making
sure that we switch to it only for the supported directions (recording
and/or playback).
For more information, please refer to 2ffaca551eaf ("snd_hda: Implement
automatic redirection between associations").
Sponsored by: The FreeBSD Foundation
MFC after: 1 week