app/testpmd: fix descriptor id check

app/testpmd: fix descriptor id check

The number of desc is a per queue configuration. But in the check
function, nb_txd & nb_rxd are used to check whether the desc_id is
valid. nb_txd & nb_rxd are the global configuration of number of desc.
If the queue configuration is changed by cmdline liks: "port config xx
txq xx ring_size xxx", the real value will be changed.

This patch use the real value to check whether the desc_id is valid.
And if these are not configured by user. It will use the default value
to check it, since the rte_eth_rx_queue_setup & rte_eth_tx_queue_setup
will use a default value to configure the queue if nb_rx_desc or
nb_tx_desc is zero.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>