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

src/session/session_timer.cpp

@@ -67,3 +67,9 @@ struct session *session_timer_expire_session(struct session_timer *timer, uint64
     struct session *sess = (struct session *)timeout->callback.arg;
     return sess;
 }
+
+// return interval to next required update, return 0 if no timer
+uint64_t session_timer_next_expire_interval(struct session_timer *timer)
+{
+    return timeouts_timeout(timer->timeouts);
+}