net/netvsc: fix Tx queue leak in error path

net/netvsc: fix Tx queue leak in error path

In hn_dev_tx_queue_setup() allocated memory for txq, we don't free it
when error happens and it will lead to memory leak.

We can check for tx_free_thresh at the beginning of the function to
fix it, before calling txq = rte_zmalloc_socket().

Fixes: cc0251813277 ("net/netvsc: split send buffers from Tx descriptors")
Cc: stable@dpdk.org
Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
Acked-by: Long Li <longli@microsoft.com>