Invalid packet-in generates confusing message

[ghost]

When running the basic.PacketIn test in relax mode, if we get a packet-in with data that doesn't correspond to the expected, the test fails with:

AssertionError: Packet in message not received on port 1

When it should be more like:

AssertionError: Response packet does not match send packet for port 1

This is happening because we have a packet-in, but it's not valid, so it's being ignored (relax mode). If there isn't another (valid) packet-in, the first message shows up.

I know it's technically not a wrong behavior, but a clearer message or warning such as "Received packet in message with unexpected data" could be helpful (I lost some time debugging what was going on :D).