CVE-2026-53012 nexthop: fix IPv6 route referencing IPv4 nexthop

In the Linux kernel, the following vulnerability has been resolved: nexthop: fix IPv6 route referencing IPv4 nexthop syzbot reported a panic 1 2. When an IPv6 nexthop is replaced with an IPv4 nexthop, the hasv4 flag of all groups containing this nexthop is not updated. This is because...