e1000x: Take CRC into consideration for size check

e1000x: Take CRC into consideration for size check

Section 13.7.15 Receive Length Error Count says:
>  Packets over 1522 bytes are oversized if LongPacketEnable is 0b
> (RCTL.LPE). If LongPacketEnable (LPE) is 1b, then an incoming packet
> is considered oversized if it exceeds 16384 bytes.

> These lengths are based on bytes in the received packet from
> <Destination Address> through <CRC>, inclusively.

As QEMU processes packets without CRC, the number of bytes for CRC
need to be subtracted. This change adds some size definitions to be used
to derive the new size thresholds to eth.h.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>