net: sched: fix TCF_LAYER_LINK case in tcf_get_base_ptr

TCF_LAYER_LINK and TCF_LAYER_NETWORK returned the same pointer as
skb->data points to the network header.
Use skb_mac_header instead.
Signed-off-by: NWolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/pkt_cls.h

@@ -522,7 +522,7 @@ static inline unsigned char * tcf_get_base_ptr(struct sk_buff *skb, int layer)
 {
 	switch (layer) {
 		case TCF_LAYER_LINK:
-			return skb->data;
+			return skb_mac_header(skb);
 		case TCF_LAYER_NETWORK:
 			return skb_network_header(skb);
 		case TCF_LAYER_TRANSPORT: