tg3: remove open-coded skb_cow_head.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Cc: Nithin Nayak Sujir <nsujir@broadcom.com>
Cc: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/tg3.c

@@ -7918,8 +7918,7 @@ static netdev_tx_t tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		struct iphdr *iph;
 		u32 tcp_opt_len, hdr_len;
 
-		if (skb_header_cloned(skb) &&
-		    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+		if (skb_cow_head(skb, 0))
 			goto drop;
 
 		iph = ip_hdr(skb);