net: ethernet: ave: Replace NET_IP_ALIGN with AVE_FRAME_HEADROOM

In commit 26a4676f ("arm64: mm: define NET_IP_ALIGN to 0"),
AVE controller affects this modification because the controller forces
to ignore lower 2bits of buffer start address, and make 2-byte headroom,
that is, data reception starts from (buffer + 2).

This patch defines AVE_FRAME_HEADROOM macro as hardware-specific value,
and replaces NET_IP_ALIGN with it.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: David S. Miller <davem@davemloft.net>