Provides api to set the web socket port when using the WebGL platform.

I successfully run the webgl platform on ubuntu16.04, it works great.
I found that at least two ports should be listen at run time, except primary port (webgl:port=12345), the second port which looks like it is prepared for web socket?
This port is random, and each time the program started, port not the same, can provide a api to set the web socket port?