Always wire the sysctl output buffer in sysctl_kern_proc() before
calling sysctl_out_proc(). -- fix from jhb

Move the code in fill_kinfo_thread() that gathers data from struct proc
into the new function fill_kinfo_proc_only().

Change all callers of fill_kinfo_thread() to call both
fill_kinfo_proc_only() and fill_kinfo() thread. When gathering
data from a multi-threaded process, fill_kinfo_proc_only() only needs
to be called once.

Grab sched_lock before accessing the process thread list or calling
fill_kinfo_thread().

PR: kern/84684
MFC after: 3 days