net: do not use skb_mac_header() in qdisc_pkt_len_init()

We want to remove our use of skb_mac_header() in tx paths,
eg remove skb_reset_mac_header() from __dev_queue_xmit().

Idea is that ndo_start_xmit() can get the mac header
simply looking at skb->data.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/dev.c

@@ -3735,25 +3735,25 @@ static void qdisc_pkt_len_init(struct sk_buff *skb)
 	 * we add to pkt_len the headers size of all segments
 	 */
 	if (shinfo->gso_size && skb_transport_header_was_set(skb)) {
-		unsigned int hdr_len;
 		u16 gso_segs = shinfo->gso_segs;
+		unsigned int hdr_len;
 
 		/* mac layer + network layer */
-		hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
+		hdr_len = skb_transport_offset(skb);
 
 		/* + transport layer */
 		if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
 			const struct tcphdr *th;
 			struct tcphdr _tcphdr;
 
-			th = skb_header_pointer(skb, skb_transport_offset(skb),
+			th = skb_header_pointer(skb, hdr_len,
 						sizeof(_tcphdr), &_tcphdr);
 			if (likely(th))
 				hdr_len += __tcp_hdrlen(th);
 		} else {
 			struct udphdr _udphdr;
 
-			if (skb_header_pointer(skb, skb_transport_offset(skb),
+			if (skb_header_pointer(skb, hdr_len,
 					       sizeof(_udphdr), &_udphdr))
 				hdr_len += sizeof(struct udphdr);
 		}