I wonder what the decision was to use a channel for that if it is called in that synced fashion. So I just want to use that to hook a log statement too but this puts me in a weird spot on when to know when to end the go func to consume that channel.
So IMHO the code should be extended as follows:

	if c.stateCh != nil {
		select {
		case <-ctx.Done():
		case c.stateCh <- s:
                default:
		}
	}

with the default branch we resolve the blocking issue by not blocking state changes. Of course the same could be done with a buffered channel but then the question is what is a proper size.
Feels like a:

func StateChanged(fn func(ConnState)) Option {
	return func(cfg *Config) error {
		cfg.stateFn = fn
		return nil
	}
}

would be simpler to use as we don't have the complexity managing the channel and go func when the current implementation requires it to be non-blocking anway.