Investigate the test approach for kmod and add the ptests back if appropriate.

The run-ptest script was recently dropped (1) with a comment that 
the kmod ptest coverage was removed in 2015. Back in 2015, Qi Chen 
commented that:
   
    The ptest part of kmod is removed because new version of kmod port all tests to
    use modules from module-playground instead of copying prebuilt modules to the
    repository. So, we cannot use ptest as before. Remove it so that kmod can build
    successfully.



Surely there's a way that we could run these ptests that wouldn't be
too much work to maintain.



1) https://lists.openembedded.org/g/openembedded-core/message/212650