Re-implemented the SOUND_MIXER_WRITE_MUTE and SOUND_MIXER_READ_MUTE
ioctls. These two ioctls were not part of the current version of OSS and were considered
obsolete. However, their behaviour is not the same as their old one, so this implementation
is not backwards compatible.
Older OSS versions had the MUTE ioctls take/return an integer with a value of 0 or 1,
which meant that the _whole_ mixer is unmuted or muted respectively. In my
implementation, the ioctl takes/returns a bitmask that tells us which devices are muted.
This allows us to (un)mute only the devices we want, instead of the whole mixer. The
bitmask works the same way as in DEVMASK, RECMASK and RECSRC.