GSD-2021-1002621 net: netlink: af_netlink: Prevent empty skb by adding a check on len.

net: netlink: afnetlink: Prevent empty skb by adding a check on len. 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 v4.9.294 by commit...