Fix issues with ALSA OSS backend for firefox and chrome.

1. When read() or write() fails due to EAGAIN because no buffer is available or buffer is full, return 0 instead of failure. Else clients may simply close the device and re-open it instantly chopping the audio.
2. Implement OSS delay function to fix an issue with negative delays.
3. Use at least 16ms of HW buffer by default to avoid jitter.

Approved by: pi, jbeich