net: smsc95xx: Correct free_pkt() implementation

On further review this returns the wrong packet length from the driver.
It may not be noticed since protocols will take care of it. Fix it by
subtracting the header length from the packet length returned.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/usb/eth/smsc95xx.c

@@ -998,7 +998,7 @@ int smsc95xx_eth_recv(struct udevice *dev, int flags, uchar **packetp)
 	}
 
 	*packetp = ptr + sizeof(packet_len);
-	return packet_len;
+	return packet_len - 4;
 
 err:
 	usb_ether_advance_rxbuf(ueth, -1);
@@ -1009,7 +1009,7 @@ static int smsc95xx_free_pkt(struct udevice *dev, uchar *packet, int packet_len)
 {
 	struct smsc95xx_private *priv = dev_get_priv(dev);
 
-	packet_len = ALIGN(packet_len, 4);
+	packet_len = ALIGN(packet_len + sizeof(u32), 4);
 	usb_ether_advance_rxbuf(&priv->ueth, sizeof(u32) + packet_len);
 
 	return 0;