MEDIUM: ssl: rename the struct "cert_key_and_chain" to "ckch_data"

Rename the structure "cert_key_and_chain" to "ckch_data" in order to
avoid confusion with the store whcih often called "ckchs".

The "cert_key_and_chain *ckch" were renamed "ckch_data *data", so we now
have store->data instead of ckchs->ckch.

Marked medium because it changes the API.
7 files changed