hdspmixer: Hardware output loopback toggle buttons

[GitHub pull_request - edited]

alsa-project/alsa-tools pull request #4 was edited from pfandl:

Hi, as promised in the sound/pci/rme9652 patch here are the user land changes which provide the user the ability to toggle the hardware output loopback functionality per output channel. I tried to hide the buttons for devices which do not expose the snd controls yet, but due to probably unnecessary struggle i cancelled that. Please let me know though should you want them removed for not yet enabled devices.

Request URL   : https://github.com/alsa-project/alsa-tools/pull/4
Patch URL     : https://github.com/alsa-project/alsa-tools/pull/4.patch
Repository URL: https://github.com/alsa-project/alsa-tools