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 v4.19.265 by commit b736592de2aa53aee2d48d6b129bc0c892007bbe, it was introduced in version v4.19.257 by commit 05fdce1ae744dee43c9181fd063c9c0db4f777f2. For more details please see the references link.