CRAS: test_client - Add capture mute option.
CRAS: test_client - Add capture mute option.

Needed to test capture mute, which was broken for some USB devices.

BUG=chromium:275863
TEST=use test client to mute input while recording.

Change-Id: I4f5a53cb96e5415a93fbed7c6c2f475ffbb95c60
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/66709

drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd