Local service interruption via expectation-dump refcount leak

Improper reference counting in Linux netfilter allows local users to exhaust kernel memory through repeated ctnetlink expectation dumps. In nf_conntrack_netlink.c, dump resumption can revisit the saved last expectation and increment its reference count twice instead of retaining only a cookie, leaking the object. Low-privileged local access is required; repeated reachable dumps consume memory and can interrupt service without reported data disclosure or modification.