vlan: make a new function vlan_dev_vlan_proto() and export

The vlan support 2 proto: 802.1q and 802.1ad, so make a new function
called vlan_dev_vlan_proto() which could return the vlan proto for
input dev.
Signed-off-by: NDing Tianhong <dingtianhong@huawei.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/if_vlan.h

@@ -110,6 +110,7 @@ extern struct net_device *__vlan_find_dev_deep(struct net_device *real_dev,
 					       __be16 vlan_proto, u16 vlan_id);
 extern struct net_device *vlan_dev_real_dev(const struct net_device *dev);
 extern u16 vlan_dev_vlan_id(const struct net_device *dev);
+extern __be16 vlan_dev_vlan_proto(const struct net_device *dev);
 
 /**
  *	struct vlan_priority_tci_mapping - vlan egress priority mappings
@@ -216,6 +217,12 @@ static inline u16 vlan_dev_vlan_id(const struct net_device *dev)
 	return 0;
 }
 
+static inline __be16 vlan_dev_vlan_proto(const struct net_device *dev)
+{
+	BUG();
+	return 0;
+}
+
 static inline u16 vlan_dev_get_egress_qos_mask(struct net_device *dev,
 					       u32 skprio)
 {

net/8021q/vlan_core.c

@@ -106,6 +106,12 @@ u16 vlan_dev_vlan_id(const struct net_device *dev)
 }
 EXPORT_SYMBOL(vlan_dev_vlan_id);
 
+__be16 vlan_dev_vlan_proto(const struct net_device *dev)
+{
+	return vlan_dev_priv(dev)->vlan_proto;
+}
+EXPORT_SYMBOL(vlan_dev_vlan_proto);
+
 static struct sk_buff *vlan_reorder_header(struct sk_buff *skb)
 {
 	if (skb_cow(skb, skb_headroom(skb)) < 0)