CVE-2026-98873: netfilter: nf_conntrack_expect: zero at allocation time

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nfconntrackexpect: zero at allocation time

There are occasional LLM hints wrt. leaking uninitialized data to userspace via ctnetlink. Just zero at allocation time, expectations are not frequently used these days.

Intentionally keeps init as-is because we could theoretically support re-init, so add the missing exp->dir there.