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>

hw/net/e1000x_common.c

@@ -140,16 +140,16 @@ bool e1000x_hw_rx_enabled(uint32_t *mac)
 
 bool e1000x_is_oversized(uint32_t *mac, size_t size)
 {
+    size_t header_size = sizeof(struct eth_header) + sizeof(struct vlan_header);
     /* this is the size past which hardware will
        drop packets when setting LPE=0 */
-    static const int maximum_ethernet_vlan_size = 1522;
+    size_t maximum_short_size = header_size + ETH_MTU;
     /* this is the size past which hardware will
        drop packets when setting LPE=1 */
-    static const int maximum_ethernet_lpe_size = 16 * KiB;
+    size_t maximum_large_size = 16 * KiB - ETH_FCS_LEN;
 
-    if ((size > maximum_ethernet_lpe_size ||
-        (size > maximum_ethernet_vlan_size
-            && !(mac[RCTL] & E1000_RCTL_LPE)))
+    if ((size > maximum_large_size ||
+        (size > maximum_short_size && !(mac[RCTL] & E1000_RCTL_LPE)))
         && !(mac[RCTL] & E1000_RCTL_SBP)) {
         e1000x_inc_reg_if_not_full(mac, ROC);
         trace_e1000x_rx_oversized(size);

include/net/eth.h

@@ -32,6 +32,8 @@
 #define ETH_ALEN 6
 #define ETH_HLEN 14
 #define ETH_ZLEN 60     /* Min. octets in frame without FCS */
+#define ETH_FCS_LEN 4
+#define ETH_MTU 1500
 
 struct eth_header {
     uint8_t  h_dest[ETH_ALEN];   /* destination eth addr */