sndio on Linux is missing output.mute

Hi list,

I've been using sndio on OpenBSD for a while now, and I've also set it
up on my Linux machine too. Surprisingly it was easier to set up than
pulseaudio which is boasted to be the best sound server on Linux if
you want something that "just works".

However I've noticed that the "output.mute" option is absent from
sndioctl on Linux, why is this?

 ~Jeremy