app/testpmd: rework display of Rx descriptors
app/testpmd: rework display of Rx descriptors

i40e supports 16 and 32 bytes RX descriptors which can be configured.
It needs to check the driver type and the configuration to determine
if 16 or 32 bytes RX descriptors is being used, for reading and
displaying the different sizes of RX descriptors.

Signed-off-by: Helin Zhang <aba9dfdb1a6ec8bf1ff66b95272c029f8dfde1b1@intel.com>
Acked-by: Jing Chen <2b730c2e01419ef3cbe586e212d13b674b74d017@intel.com>
Acked-by: Cunming Liang <7edc6dd0948177c688da9b288939d80da3db4303@intel.com>

phermansson/dpdk,phermansson/dpdk,phermansson/dpdk,phermansson/dpdk