net: ethernet: mediatek: Use NET_IP_ALIGN to judge if HW RX_2BYTE_OFFSET is enabled

Should only enable HW RX_2BYTE_OFFSET function in the case NET_IP_ALIGN
equals to 2.

Signed-off-by: Mark Lee <mark-mc.lee@mediatek.com>
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>