hw/net/lan9118: Replace magic '2048' value by MIL_TXFIFO_SIZE definition

The magic 2048 is explained in the LAN9211 datasheet (DS00002414A)
in chapter 1.4, "10/100 Ethernet MAC":

  The MAC Interface Layer (MIL), within the MAC, contains a
  2K Byte transmit and a 128 Byte receive FIFO which is separate
  from the TX and RX FIFOs. [...]

Note, the use of the constant in lan9118_receive() reveals that
our implementation is using the same buffer for both tx and rx.

Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Message-Id: <[email protected]>

Author: philmd

hw/net/lan9118.c

@@ -150,6 +150,12 @@ do { printf("lan9118: " fmt , ## __VA_ARGS__); } while (0)
 
 #define GPT_TIMER_EN    0x20000000
 
+/*
+ * The MAC Interface Layer (MIL), within the MAC, contains a 2K Byte transmit
+ * and a 128 Byte receive FIFO which is separate from the TX and RX FIFOs.
+ */
+#define MIL_TXFIFO_SIZE         2048
+
 enum tx_state {
     TX_IDLE,
     TX_B,
@@ -166,7 +172,7 @@ typedef struct {
     int32_t pad;
     int32_t fifo_used;
     int32_t len;
-    uint8_t data[2048];
+    uint8_t data[MIL_TXFIFO_SIZE];
 } LAN9118Packet;
 
 static const VMStateDescription vmstate_lan9118_packet = {
@@ -182,7 +188,7 @@ static const VMStateDescription vmstate_lan9118_packet = {
         VMSTATE_INT32(pad, LAN9118Packet),
         VMSTATE_INT32(fifo_used, LAN9118Packet),
         VMSTATE_INT32(len, LAN9118Packet),
-        VMSTATE_UINT8_ARRAY(data, LAN9118Packet, 2048),
+        VMSTATE_UINT8_ARRAY(data, LAN9118Packet, MIL_TXFIFO_SIZE),
         VMSTATE_END_OF_LIST()
     }
 };
@@ -544,7 +550,7 @@ static ssize_t lan9118_receive(NetClientState *nc, const uint8_t *buf,
         return -1;
     }
 
-    if (size >= 2048 || size < 14) {
+    if (size >= MIL_TXFIFO_SIZE || size < 14) {
         return -1;
     }