net/hns3: fix checking enough Tx BDs

net/hns3: fix checking enough Tx BDs

In .tx_pkt_burst ops implementation function of hns3 PMD driver,
there is one check whether there are enough BDs in the TX queue.
If not, driver will stop sending the packets.

Currently in the 'for' process loop, the next_to_use member of
TX queue is not updated in time after processing BDs of one packet,
which results in the invalid action of checking whether there are
enough BDs and failure in sending packets.

This patch fixes it by moving the assignment statment of the
next_to_use member of TX queue to the place after porcessing TX BDs
in the 'for' loop.

Fixes: bba636698316 ("net/hns3: support Rx/Tx and related operations")
Cc: stable@dpdk.org
Signed-off-by: Hongbo Zheng <zhenghongbo3@huawei.com>
Signed-off-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>