l2t_skb_cb
struct l2t_skb_cb *cb = L2T_SKB_CB(skb);
#define L2T_SKB_CB(skb) ((struct l2t_skb_cb *)(skb)->cb)
const struct l2t_skb_cb *cb = L2T_SKB_CB(skb);
#define L2T_SKB_CB(skb) ((struct l2t_skb_cb *)(skb)->cb)
struct l2t_skb_cb l2t; /* reserve space for l2t CB */
struct l2t_skb_cb l2t;