net: Export netif_get_vlan_features().

ERROR: "netif_get_vlan_features" [drivers/net/xen-netfront.ko] undefined!
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -1983,6 +1983,7 @@ int netif_get_vlan_features(struct sk_buff *skb, struct net_device *dev)
 	else
 		return 0;
 }
+EXPORT_SYMBOL(netif_get_vlan_features);
 
 /*
  * Returns true if either: