ng_l2cap_new_chan
ch = ng_l2cap_new_chan(l2cap, con, psm);
ng_l2cap_chan_p ng_l2cap_new_chan (ng_l2cap_p, ng_l2cap_con_p, u_int16_t);
ch = ng_l2cap_new_chan(l2cap, con, ip->psm);