session manager: support session timeouts & tcp dupkt filter & udp eviction filter

src/session/session_timer.h

@@ -18,6 +18,8 @@ void session_timer_del_session(struct session_timer *timer, struct session *sess
  * if return session, the session will be removed from timer.
  */
 struct session *session_timer_expire_session(struct session_timer *timer, uint64_t abs_current_ts);
+// return interval to next required update, return 0 if no timer
+uint64_t session_timer_next_expire_interval(struct session_timer *timer);
 
 #ifdef __cpluscplus
 }