[client] audio: reduce hardcoded minimum latency

The current minimum target latency is partially based upon the default qemu
behaviour whereby audio packets are delivered in a sawtooth pattern, with
packet timestamps drifting between 5ms above and below the measured clock.
This 5ms error is baked into the minimum target latency to avoid
underrunning.

This sawtooth pattern can be reduced by specifying a lower timer period in
the qemu configuration, so remove it from the hardcoded minimum latency and
add it to the default configurable buffer latency instead. This allows
users that have configured their VM appropriately to reduce the overall
latency.

client/src/config.c

@@ -478,7 +478,7 @@ static struct Option options[] =
     .name           = "bufferLatency",
     .description    = "Additional buffer latency in milliseconds",
     .type           = OPTION_TYPE_INT,
-    .value.x_int    = 8
+    .value.x_int    = 13
   },
   {0}
 };