* Make sure we set oldlenp based on rlen.
* If we get no response buffer but we do have the length then set it to that.
  The "how big is X?" API involves doing a query for an OID, with no old buffer
  but with an oldlenp set.  The size of the response is then put in oldlenp.
I'm now hacking on the freebsd supplied sysctl; move the old sysctl.c out of the way.
Try to handle the case where no oldp buffer is provided, but we do want
the resulting length.