Bugfix in ps usage for sl, optimized tcap_higher_prio and fixed asnd/rcv test in micro_booter

[phanikishoreg]

Summary of this Pull Request (PR)

Fixes & changes: KERNEL:

• optimized tcap_higher_prio to return immediately if both tcaps are same, return 1 to preempt the current.

SCHEDLIB:

• bugfix in ps library usage - use ps_list_is_head to check if there are no items in the list.

MICROBOOTER:

• fixed asnd/rcv unit test case, parent must be higher and child must be lower for the test we have in there. It worked because of preemption stack feature mainly. I'm sorry I missed the error in the test output somehow!

Intent for your PR

Choose one (Mandatory):

• [ ] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
• [x] This PR is mature, and ready to be integrated into the repo.

Reviewers (Mandatory):

@gparmer

Code Quality

As part of this pull request, I've considered the following:

Style:

• [x] Comments adhere to the Style Guide (SG)
• [x] Spacing adhere's to the SG
• [x] Naming adhere's to the SG
• [x] All other aspects of the SG are adhered to, or exceptions are justified in this pull request
• [ ] I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions)

Code Craftsmanship:

• [x] I've made an attempt to remove all redundant code
• [x] I've considered ways in which my changes might impact existing code, and cleaned it up
• [x] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• [x] I've commented appropriately where code is tricky
• [x] I agree that there is no "throw-away" code, and that code in this PR is of high quality

Testing

I've tested the code using the following test programs (provide list here):

• micro_booter, vkernel_booter, unit_schedtest, unit_fprr, unit_defci
• also hierarchical sl scheduling in rump2cos.

[gparmer]

:+1: