Doctests for the `kernel` crate

configname: CONFIG_RUST_KERNEL_DOCTESTS

Linux Kernel Configuration
└─>Kernel hacking
└─>Rust hacking
└─>KUnit - Enable support for unit tests
└─>Doctests for the `kernel` crate
In linux kernel since version 4.14.327 (release Date: 2023-10-10)  
This builds the documentation tests of the `kernel` crate
as KUnit tests.

For more information on KUnit and unit tests in general,
please refer to the KUnit documentation in