taskqueues, more than one task can be running simultaneously.
Also make taskqueue_run(9) static to the file, since there are no
consumers in the base kernel and the function signature needs to change
with this fix.
Remove mention of taskqueue_run(9) and taskqueue_run_fast(9) from the
taskqueue(9) man page.
Reviewed by: jhb
Approved by: zml (mentor)