Can we max out the multiplex layer?

[yaronyg]

There have to be practical limits on things like how many streams we can ever create in the same multiplex session and possibly how many streams can be simultaneously alive (if only not to cause a memory failure). We need to figure out what these limits are and make sure they don't cause security overflow style issues (or a weak DOS) and that we handle closing the connection and creating a new mux channel properly when needed.