we should reduce the frame buffer size in NewWebsocket

For compatibility with clients that didn't support framing, when we introduced the new gorilla websockets, we used 64kB buffers. However, that is now a significant source of memory overhead.

Since gorilla supports message frames, and we no longer need to worry about 2.1 agents/clients against a new controller, we should be able to drop the buffers back to their default 4096 bytes.

We need to do cross-version testing with reasonably large messages to convince ourselves that the frames are working correctly, but that should reduce one of our primary sources of memory consumption.