e1000e: fixup merge error

When merging into Jeff's tree:

	commit 5f66f208
	Author: Arthur Jones <ajones@riverbed.com>
	Date:   Thu Mar 19 01:13:08 2009 +0000

	    e1000e: allow tx of pre-formatted vlan tagged packets

We lost one line, this fixes that missing
piece...
Signed-off-by: NArthur Jones <ajones@riverbed.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/e1000e/netdev.c

@@ -3774,7 +3774,7 @@ static bool e1000_tx_csum(struct e1000_adapter *adapter, struct sk_buff *skb)
 	else
 		protocol = skb->protocol;
 
-	switch (skb->protocol) {
+	switch (protocol) {
 	case cpu_to_be16(ETH_P_IP):
 		if (ip_hdr(skb)->protocol == IPPROTO_TCP)
 			cmd_len |= E1000_TXD_CMD_TCP;