make sure the "overload_tbl" member of "struct pf_rule" copied in
from userland is initialized (it is used by the kernel only)
fixes crash or data injection (CVE-2010-3830), usually by root user only
OpenBSD has rewritten the code to start with a zero'd struct and fills
in needed parts only - to be considered in case a newer pf version
is imported.

(drochner)