net: hns3: fix for skb leak when doing selftest

If hns3_nic_net_xmit does not return NETDEV_TX_BUSY when doing
a loopback selftest, the skb is not freed in hns3_clean_tx_ring
or hns3_nic_net_xmit, which causes skb not freed problem.

This patch fixes it by freeing skb when hns3_nic_net_xmit does
not return NETDEV_TX_OK.

Fixes: c39c4d98 ("net: hns3: Add mac loopback selftest support in hns3 driver")

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>