allowing multiple calls to cxy_ctl:init/1

Hey :)

I have the following use case, where an application has multiple dependencies trying to set their own concurrency limits. I've figured that it wouldn't hurt to allow multiple calls to cxy_ctl:init/1, so each dependency could allow its own concurrency limits along the way (and/or adding limits when needed, instead of being a one-time only operation).

Makes sense?