tcp_req_free_a_slot
tcp_req_free_a_slot(rack->rc_tp, ent);
tcp_req_free_a_slot(tp, ent);
tcp_req_free_a_slot(tp, ent);
tcp_req_free_a_slot(tp, ent);
void tcp_req_free_a_slot(struct tcpcb *tp, struct tcp_sendfile_track *ent);