tsnep: Fix TX queue stop/wake for multiple queues

netif_stop_queue() and netif_wake_queue() act on TX queue 0. This is ok
as long as only a single TX queue is supported. But support for multiple
TX queues was introduced with 76203137 and I missed to adapt stop
and wake of TX queues.

Use netif_stop_subqueue() and netif_tx_wake_queue() to act on specific
TX queue.

Fixes: 76203137

 ("tsnep: Support multiple TX/RX queue pairs")
Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
Link: https://lore.kernel.org/r/20230124191440.56887-1-gerhard@engleder-embedded.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>