MFC kern_proc.c - fix locking in sysctl_kern_proc()

MFC kern_proc.c - fix locking in sysctl_kern_proc()

Original commit message:

  FreeBSD src repository

  Modified files:
    sys/kern             kern_proc.c
  Log:
  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
Approved by:	re (scottl)