Increase WebSocket message size limit in websocket-server

I'm seeing this being logged in frequently:

error copying WebSocket to ORPort: frame payload length of 8926 exceeds maximum of 2500
error copying WebSocket to ORPort: frame payload length of 4244 exceeds maximum of 2500
error copying WebSocket to ORPort: frame payload length of 2928 exceeds maximum of 2500

8926 is the biggest I saw. Increase the limit so this doesn't happen. Probably need to increase the limit in flashproxy-client too. Also update websocket-transport.txt.