Use the kref API

[l0kod]

Landlock currently uses refcount_t types, but it would be better to use struct kref and the related helpers instead.

[Madhupatel08]

Hi @l0kod,
can you assign this task to me, I'm working on it, and will raise a PR by tomorrow

[l0kod]

Hi @Madhupatel08! Looking at the consequence of using kref in the current code, I'm starting to think it may not be a good idea because it could increase code complexity for not much benefit. However, you can still send a patch with this change and we'll discuss on the mailing list with other reviewers looking at concret code. Anyway, it would still be a good first start if this is for Outreachy.

FYI, the Linux kernel doesn't work with PRs but patches sent by emails as explained in the documentation.

[l0kod]

As discussed offline, we should spend time on other tasks such as #19 or #23 .