Some resources can't unset values in UpdateOpts

[mandre]

What happened?

While working on resource mutability for ORC, we've experienced multiple cases where gophercloud allows updating a property, but not unsetting it. This issue is meant to keep track of the ones we noticed so that we can make the necessary changes for the upcoming major gophercloud version.

• Volume metadata
• Floating IP fixed IP

They're all caused by a missing pointer. We should conduct a full review of all the UpdateOpts and make the necessary code changes before releasing v3.

Version

v2 (current)

[mandre]

This would be a continuation of the work done with https://github.com/gophercloud/gophercloud/pull/3190.