session add API support get/set closing reasion

src/session/session_private.h

@@ -49,6 +49,9 @@ struct session
     // session type
     enum session_type type;
 
+    // closing reasion
+    enum closing_reasion closing_reasion;
+
     // session metrics
     uint64_t c2s_bytes;
     uint64_t s2c_bytes;