CVE-2026-97940 ipv6: fix fib6 walker UAF on seq stop

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix fib6 walker UAF on seq stop ipv6routeiteractive treats a walker in FWSU at the table root as already unlinked. fib6delroute can move a still-linked walker into that same state when the current leaf is the last route at...