CVE-2026-52940 tun: zero the whole vnet header in tun_put_user()

In the Linux kernel, the following vulnerability has been resolved: tun: zero the whole vnet header in tunputuser tunputuser declares an on-stack struct virtionethdrv1hashtunnel without zeroing it. For a non-tunnel skb, virtionethdrtnlfromskb only initializes the first 10 bytes sizeofstruct...