Problem/Motivation
Spinning this out from #126197: Option to Disable IP Logging.
Drupal permanently logs IP addresses and has done so for at least ten years. This isn't used for anything by default, it's just stored away.
#126197: Option to Disable IP Logging adds a privacy module which would anonymise IP addresses - this is great for things like flood control and similar where the IP address is used for a specific reason (i.e. we need to store a unique identifier for the duration of a request). However comment module just doesn't need to store IP addresses at all - the fact it's linked directly and permanently with e-mail addresses/user accounts makes it different from log/flood etc. too
Proposed resolution
Add a configuration setting to control whether IP addresses are logged or not. Default this to off for new sites but add an update to leave it on for existing sites - we can add a change record to let existing sites know they can change it themselves.
This will be compatible with the privacy module - you could re-enable IP logging and have privacy module installed, in which case comments get associated with a unique identifier, just not the actual IP address - still useful for identifying sock puppet accounts on social sites and similar.