Fix memfd_secrete selftest

[musamaanjum]

The test is failing consistently. For example: https://linux.kernelci.org/test/plan/id/657654bd8e81e654fae13532/

The bug happens when the max locked memory limit is increased beyond a certain limit. Initially, I was thinking that only the test was wrong. It isn't robust enough. But as I've investigated, there is something wrong with the kernel as well. There is 1-page difference between how many pages can be locked and how many kernel says can be locked. The difference is 1024 bytes if we look at raw numbers before certain calculations. I'm investigating this further.

[musamaanjum]

Closing the ticket as we aren't tracking bugs found in the kernel in this project anymore.