CVE-2026-31504: In the Linux kernel, the following vulnerability has been resolved: net: fix fanout UAF in packet_release() via NETDEV_

A race condition vulnerability exists in the Linux kernel's packet networking code where `packet_release()` can leave a dangling pointer in a fanout group's array (a data structure for managing network packet distribution). The problem occurs because `NETDEV_UP` (a network device startup event) can re-register a socket into the array after `packet_release()` begins cleanup but before it finishes, creating a use-after-free bug (accessing memory that has been freed).