sndioctl: support change input level

[catap]

This new version was tested on two devices:

The first one:

input.level=0.694
input.mute=0
output.level=0.631
output.mute=0
server.device=0(azalia0)

And the second one

output.level=1.000
output.mute=0
server.device=1(uaudio0)

With and without input channel