Bump up default RTP player buffer sizes. Now big enough to keep ALSA

(first doubling) and ALSA's OSS emulation (second doubling) fed.  The
initial buffer size is still under half a second, and feels close to
instant to this listener.

Also, the player thread now consumes packets immediately rather than
waiting for the next iteration, preventing a race where the (inner)
playing loop at the bottom of main() can terminate unnecessarily
early.

There's bits of debugging code left lying around commented out.  It's
harmless for now!