Update the sysctl_ctx_init(9) manual page with the following
information from the submitter:

Starting value for OID_AUTO was changed from 100 to 256 (0x100) in
kern/kern_sysctl.c#rev1.112 on 2001-07-25, and defined as
CTL_AUTO_START in sys/sysctl.h#rev1.98.

Submitted by: cnst
Silence from: #bsddocs on efnet
MFC After: 3 days
Approved by: re (bmah)