ip_tunnels: allow VXLAN/GENEVE to inherit TOS/TTL from VLAN

The current code allows for VXLAN and GENEVE to inherit the TOS
respective the TTL when skb-protocol is ETH_P_IP or ETH_P_IPV6.
However when the payload is VLAN encapsulated, then this inheriting
does not work, because the visible skb-protocol is of type
ETH_P_8021Q or ETH_P_8021AD.

Instead of skb->protocol use skb_protocol().
Signed-off-by: Matthias May <matthias.may@westermo.com>
Link: https://lore.kernel.org/r/20220721202718.10092-1-matthias.may@westermo.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/ip_tunnels.h

@@ -387,9 +387,11 @@ static inline int ip_tunnel_encap(struct sk_buff *skb, struct ip_tunnel *t,
 static inline u8 ip_tunnel_get_dsfield(const struct iphdr *iph,
 				       const struct sk_buff *skb)
 {
-	if (skb->protocol == htons(ETH_P_IP))
+	__be16 payload_protocol = skb_protocol(skb, true);
+
+	if (payload_protocol == htons(ETH_P_IP))
 		return iph->tos;
-	else if (skb->protocol == htons(ETH_P_IPV6))
+	else if (payload_protocol == htons(ETH_P_IPV6))
 		return ipv6_get_dsfield((const struct ipv6hdr *)iph);
 	else
 		return 0;
@@ -398,9 +400,11 @@ static inline u8 ip_tunnel_get_dsfield(const struct iphdr *iph,
 static inline u8 ip_tunnel_get_ttl(const struct iphdr *iph,
 				       const struct sk_buff *skb)
 {
-	if (skb->protocol == htons(ETH_P_IP))
+	__be16 payload_protocol = skb_protocol(skb, true);
+
+	if (payload_protocol == htons(ETH_P_IP))
 		return iph->ttl;
-	else if (skb->protocol == htons(ETH_P_IPV6))
+	else if (payload_protocol == htons(ETH_P_IPV6))
 		return ((const struct ipv6hdr *)iph)->hop_limit;
 	else
 		return 0;