sch_cake: do not use skb_mac_header() in cake_overhead()

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/sched/sch_cake.c

@@ -1360,7 +1360,7 @@ static u32 cake_overhead(struct cake_sched_data *q, const struct sk_buff *skb)
 		return cake_calc_overhead(q, len, off);
 
 	/* borrowed from qdisc_pkt_len_init() */
-	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 |
@@ -1368,14 +1368,14 @@ static u32 cake_overhead(struct cake_sched_data *q, const struct sk_buff *skb)
 		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);
 	}