Drivers should reserve some headroom in skb used in receive path,
to avoid future head reallocation.

One possible way to do that is to use dev_alloc_skb() instead
of alloc_skb(), so that NET_SKB_PAD bytes are reserved.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>