optimizate inject packt test case

src/session/session_manager.cpp

@@ -298,8 +298,6 @@ static void tcp_update(struct session_manager *mgr, struct session *sess, enum f
      {
           half->isn = tcp_hdr_get_seq(hdr);
      }
-     half->inject_inc_ack_offset = 0;
-     half->inject_inc_seq_offset = 0;
      half->flags = flags;
      half->history |= flags;
      half->seq = tcp_hdr_get_seq(hdr);