virtio-net: zero unused hash fields

When GSO tunnel is negotiated virtio_net_hdr_tnl_from_skb() tries to
initialize the tunnel metadata but forget to zero unused rxhash
fields. This may leak information to another side. Fixing this by
zeroing the unused hash fields.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Fixes: a2fb4bc4 ("net: implement virtio helpers to handle UDP GSO tunneling")
Cc: <stable@vger.kernel.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Link: https://patch.msgid.link/20251022034421.70244-1-jasowang@redhat.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>