MFH: r414376

audio/alsa-lib: improve etc/asound.conf

• Expose "oss" via "aplay -L"
• Simplify "oss" and "pulse"
• Define "sysdefault"

Note, "aplay -D sysdefault" != "aplay -D oss" per ports/184006

Approved by: ports-secteam (junovitch)