virtio_net: formalize skb_vnet_hdr
virtio_net: formalize skb_vnet_hdr

We put the virtio_net_hdr into the skb's cb region; turn this into a
union to clean up the code slightly and allow future expansion.

Signed-off-by: Rusty Russell <df9728c9e5104131c08c7adb03af425394842596@rustcorp.com.au>
Cc: Mark McLoughlin <c437454578aa740e24bc1bc37b06380de7125486@redhat.com>
Cc: Dinesh Subhraveti <04fecee2d584355630b7ffb714c57299dcbdd605@us.ibm.com>

KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs