message: [test] P2P connection behavior should meet expectations
  P2PTxInvStore should supplement `on_inv` behavior of parent, not overwrite.
diff: @@ -655,6 +655,8 @@ class P2PTxInvStore(P2PInterface):
  # save txid
  self.tx_invs_received[i.hash] += 1
  + super().on_inv(message)
  +
  def get_invs(self):
  with mininode_lock:
  return list(self.tx_invs_received.keys())
  