fix streaming cache size

The streaming cache size is supposed to be 16 MiB, somehow on master it's 65 KiB. That would explain why performance was crawling for everyone who tried it.

At 16 MiB I'm seeing streaming speeds as much as 100mbps, which should be enough to accommodate a 4K stream. To get that 100mbps number higher, we'd either need to increase the cache size (which would adversely impact seek times on applications with large buffers, like mpv) or we need to improve our download latency.

My guess is that we can improve our download latency by a factor of 2 or more with not too much effort, which should be enough to get our streaming endpoint to 200mbps+ even with the smaller cache size.