- Add a sysctl to allow non-root users the ability to set idle priorities.
- Add a sysctl to allow non-root users the ability to set idle
priorities.

- While here fix up some style nits.

Discussed with: cperciva (breifly)
Reviewed by:	pjd (earlier version)
Reviewed by:	bde
Approved by:	jhb
MFC after:	1 month

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