The uses of uint8_t pointers were misleading as they are never accessed
as an array of octets and it even require more strict alignment to
access as struct eth_header.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>