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 v5.4.224 by commit b49f6b2f21f543d4dc88fb7b1ec2adccb822f27c, it was introduced in version v5.4.212 by commit 51be9dd391fd25872b95708a0250f2f7722d2d8e. For more details please see the references link.