net/ring: do not count unsent packets as errors

net/ring: do not count unsent packets as errors

err_pkts reflects the number of packets that the driver did not manage
to send.
This is a temporary situation, those packets are not freed and the
application can still retry to send them later.
Hence, we can't count them as transmit failed.

Fixes: e1e4017751f1 ("ring: add new driver")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>