Add session state 'discard'

src/session/session_transition.h

@@ -28,6 +28,9 @@ enum session_inputs
 
     // session table full evict
     LRU_EVICT = 1 << 7,
+
+    // user close
+    USER_CLOSE = 1 << 8,
 };
 
 void session_transition_init();