net/hns3: optimize Tx performance
net/hns3: optimize Tx performance

This patch uses tx_free_thresh to control mbufs free when the common
xmit algorithm is used.

This patch also modifies the implementation of PMD's tx_done_cleanup
because the mbuf free algorithm changed.

In the testpmd single core MAC forwarding scenario, the performance is
improved by 10% at 64B on Kunpeng920 platform.

Cc: stable@dpdk.org

Signed-off-by: Chengwen Feng <af69652d70a703aa3bb4268f61750255b6f8fb91@huawei.com>
Signed-off-by: Min Hu (Connor) <f02e10cb0a484c51b0f8634f83fbb4ab9ded1c6a@huawei.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk