asix: Fix tx transfer padding for full-speed USB

The asix.c USB Ethernet driver avoids ending a tx transfer with a zero-
length packet by appending a four-byte padding to transfers whose length
is a multiple of maxpacket. However, the hard-coded 512 byte maxpacket
length is valid for high-speed USB only; full-speed USB uses 64 byte
packets.
Signed-off-by: NIngo van Lil <inguin@gmx.de>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/asix.c

@@ -355,7 +355,7 @@ static struct sk_buff *asix_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
 	u32 packet_len;
 	u32 padbytes = 0xffff0000;
 
-	padlen = ((skb->len + 4) % 512) ? 0 : 4;
+	padlen = ((skb->len + 4) & (dev->maxpacket - 1)) ? 0 : 4;
 
 	if ((!skb_cloned(skb)) &&
 	    ((headroom + tailroom) >= (4 + padlen))) {
@@ -377,7 +377,7 @@ static struct sk_buff *asix_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
 	cpu_to_le32s(&packet_len);
 	skb_copy_to_linear_data(skb, &packet_len, sizeof(packet_len));
 
-	if ((skb->len % 512) == 0) {
+	if (padlen) {
 		cpu_to_le32s(&padbytes);
 		memcpy(skb_tail_pointer(skb), &padbytes, sizeof(padbytes));
 		skb_put(skb, sizeof(padbytes));