Your options are very limited. Browsers which support WebSockets expect the server to speak WebSocket to them (which involves participating in a 2-way handshake). Communicating in raw UDP is an entirely different kettle of fish.
Chrome has experimental support for raw UDP, but only for Chrome extensions.
I don't know of any other browser with this in the works, or for Chrome to make it available for websites.
Your best best would be to change your endpoint to talk WebSocket, or to use a middleman server (NodeJS would be great for this) to handle the Websocket <-> raw UDP conversion.