sundance: Fix oopses with corrupted skb_shared_info

Joel Soete reported oopses at the beginning of pppoe connections since
v2.6.35. After debugging the bug was found in sundance skb allocation
and dma mapping code, where skb_reserve() bytes aren't taken into
account. This is an old bug, only uncovered by some change in 2.6.35.

Initial debugging patch by: Eric Dumazet <eric.dumazet@gmail.com>
Reported-by: NJoel Soete <soete.joel@scarlet.be>
Tested-by: NJoel Soete <soete.joel@scarlet.be>
Signed-off-by: NJarek Poplawski <jarkao2@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/sundance.c

@@ -1016,7 +1016,7 @@ static void init_ring(struct net_device *dev)
 
 	/* Fill in the Rx buffers.  Handle allocation failure gracefully. */
 	for (i = 0; i < RX_RING_SIZE; i++) {
-		struct sk_buff *skb = dev_alloc_skb(np->rx_buf_sz);
+		struct sk_buff *skb = dev_alloc_skb(np->rx_buf_sz + 2);
 		np->rx_skbuff[i] = skb;
 		if (skb == NULL)
 			break;
@@ -1407,7 +1407,7 @@ static void refill_rx (struct net_device *dev)
 		struct sk_buff *skb;
 		entry = np->dirty_rx % RX_RING_SIZE;
 		if (np->rx_skbuff[entry] == NULL) {
-			skb = dev_alloc_skb(np->rx_buf_sz);
+			skb = dev_alloc_skb(np->rx_buf_sz + 2);
 			np->rx_skbuff[entry] = skb;
 			if (skb == NULL)
 				break;		/* Better luck next round. */