net/usbnet: reserve headroom on rx skbs

net/usbnet: reserve headroom on rx skbs

network drivers should reserve some headroom on incoming skbs so that we
dont need expensive reallocations, eg forwarding packets in tunnels.

This NET_SKB_PAD padding is done in various helpers, like
__netdev_alloc_skb_ip_align() in this patch, combining NET_SKB_PAD and
NET_IP_ALIGN magic.

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Oliver Neukum <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Acked-by: Oliver Neukum <[email protected]>
Signed-off-by: David S. Miller <[email protected]>