l2tp_ip_sk
l2tp_ip_sk(sk)->conn_id = addr->l2tp_conn_id;
l2tp_ip_sk(sk)->peer_conn_id = lsa->l2tp_conn_id;
struct l2tp_ip_sock *lsk = l2tp_ip_sk(sk);
const struct l2tp_ip_sock *l2tp = l2tp_ip_sk(sk);