music_chunk: increased chunk size to 4 kB

A larger chunk size means less overhead for managing them.  4 kB seems
to be a reasonable choice: it contains 23 ms of 44.1 kHz 16 bit stereo
data, or 3 ms of 192 kHz 24 bit stereo data.  The original value of
1020 seemed to be too small, there were quite a lot of system calls
and context switches.

src/chunk.h

@@ -28,8 +28,7 @@
 #include <stddef.h>
 
 enum {
-	/* pick 1020 since its devisible for 8,16,24, and 32-bit audio */
-	CHUNK_SIZE = 1020,
+	CHUNK_SIZE = 4096,
 };
 
 struct audio_format;