net/vlan: introduce skb_vlan_tag_get_cfi() helper

Abstract CFI/DEI bit access consistently with other VLAN tag fields.
Signed-off-by: NMichał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/if_vlan.h

@@ -65,7 +65,7 @@ static inline struct vlan_ethhdr *vlan_eth_hdr(const struct sk_buff *skb)
 
 #define VLAN_PRIO_MASK		0xe000 /* Priority Code Point */
 #define VLAN_PRIO_SHIFT		13
-#define VLAN_CFI_MASK		0x1000 /* Canonical Format Indicator */
+#define VLAN_CFI_MASK		0x1000 /* Canonical Format Indicator / Drop Eligible Indicator */
 #define VLAN_VID_MASK		0x0fff /* VLAN Identifier */
 #define VLAN_N_VID		4096
 
@@ -80,6 +80,7 @@ static inline bool is_vlan_dev(const struct net_device *dev)
 #define skb_vlan_tag_present(__skb)	((__skb)->vlan_present)
 #define skb_vlan_tag_get(__skb)		((__skb)->vlan_tci)
 #define skb_vlan_tag_get_id(__skb)	((__skb)->vlan_tci & VLAN_VID_MASK)
+#define skb_vlan_tag_get_cfi(__skb)	(!!((__skb)->vlan_tci & VLAN_CFI_MASK))
 #define skb_vlan_tag_get_prio(__skb)	(((__skb)->vlan_tci & VLAN_PRIO_MASK) >> VLAN_PRIO_SHIFT)
 
 static inline int vlan_get_rx_ctag_filter_info(struct net_device *dev)