[3c90x] Fix High-MTU packet reception

Prevent the card from flagging packets of 1518 bytes length as
overlength.

This fixes the High-MTU loopback test.

Signed-off-by: Thomas Miletich <thomas.miletich@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/3c90x.c

@@ -822,6 +822,10 @@ static int a3c90x_open(struct net_device *netdev)
 
 	a3c90x_internal_IssueCommand(inf_3c90x->IOAddr, cmdStallCtl, upUnStall);
 
+	/* set maximum allowed receive packet length */
+	a3c90x_internal_SetWindow(inf_3c90x, winTxRxOptions3);
+	outl(RX_BUF_SIZE, inf_3c90x->IOAddr + regMaxPktSize_3_w);
+
 	/* enable packet transmission and reception */
 	a3c90x_internal_IssueCommand(inf_3c90x->IOAddr, cmdTxEnable, 0);
 	a3c90x_internal_IssueCommand(inf_3c90x->IOAddr, cmdRxEnable, 0);