Add lwkt_setcpu_self(), a function which migrates the current thread to

Add lwkt_setcpu_self(), a function which migrates the current thread to
the specified cpu.  This will soon be used by sysctl_kern_proc() to
collect thread information across all available cpus (because it is only
legal to manipulate a thread on the cpu it belongs to).

Yes, you heard that right and, yes, the overhead is nasty... one whole
microsecond per cpu at least, possibly even two.  But who cares for
something like 'ps'?

In-conversation-with: Hiten Pandya <hmp@freebsd.org>