net/sched: remove two skb_mac_header() uses

tcf_mirred_act() and tcf_mpls_act() can use skb_network_offset()
instead of relying on skb_mac_header().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: edumazet

net/sched/act_mirred.c

@@ -295,7 +295,7 @@ TC_INDIRECT_SCOPE int tcf_mirred_act(struct sk_buff *skb,
 	at_nh = skb->data == skb_network_header(skb);
 	if (at_nh != expects_nh) {
 		mac_len = skb_at_tc_ingress(skb) ? skb->mac_len :
-			  skb_network_header(skb) - skb_mac_header(skb);
+			  skb_network_offset(skb);
 		if (expects_nh) {
 			/* target device/action expect data at nh */
 			skb_pull_rcsum(skb2, mac_len);

net/sched/act_mpls.c

@@ -69,7 +69,7 @@ TC_INDIRECT_SCOPE int tcf_mpls_act(struct sk_buff *skb,
 		skb_push_rcsum(skb, skb->mac_len);
 		mac_len = skb->mac_len;
 	} else {
-		mac_len = skb_network_header(skb) - skb_mac_header(skb);
+		mac_len = skb_network_offset(skb);
 	}
 
 	ret = READ_ONCE(m->tcf_action);