iwlwifi: use reset to set transport header

Since offset is zero, it's not necessary to use set function. Reset
function is straightforward, and will remove the unnecessary add
operation in set function.
Signed-off-by: NZhang Shengju <zhangshengju@cmss.chinamobile.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/wireless/intel/iwlwifi/pcie/tx.c

@@ -2196,7 +2196,7 @@ static int iwl_fill_data_tbs_amsdu(struct iwl_trans *trans, struct sk_buff *skb,
 
 			memcpy(skb_put(csum_skb, tcp_hdrlen(skb)),
 			       tcph, tcp_hdrlen(skb));
-			skb_set_transport_header(csum_skb, 0);
+			skb_reset_transport_header(csum_skb);
 			csum_skb->csum_start =
 				(unsigned char *)tcp_hdr(csum_skb) -
 						 csum_skb->head;