net, neigh: Fix null-ptr-deref in neightableclear()
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.15.78 by commit 2b45d6d0c41cb9593868e476681efb1aae5078a1, it was introduced in version v5.15.65 by commit db6fa03d80ab076238fc806c9925d1f8b9639d1b. For more details please see the references link.