rename greylist in reconnect in state_point

This MR changes variable greylist to reconnect_delay.

It is similar to the !1576 (closed) but is does not change the configuration file.

This MR is only a code refactor. If this MR is accepted, then we can address the backward compatibility issue related to the config file in a different MR. This can be problematic as we don't have yet a simple and standard way to deprecate configuration options via data_encoding.

I think it's important to refactor this piece of code as it easily leads to confusion when thinking about greylisting.