testpmd behavior with stopped queues

[Dmitry Kozlyuk]

Hello,

There are testpmd commands to start/stop RxQ/TxQ:
"port 1 rxq 0 stop", "port 1 txq 0 start", etc.
IIUC, when a queue is stopped, testpmd should ignore it.
Currently, it doesn't and tries to use the stopped queue.
If a RxQ is stopped, nothing will be send to the paired TxQ.
If a TxQ is stopped, there is nowhere to send the packets
from the paired RxQ, so it is logical to drop them.
I'm going to implement this behavior, any objections?