net/failsafe: fix crash on slave queue release

net/failsafe: fix crash on slave queue release

Releasing a queue that is already released by slave may cause a
segmentation fault. For example, after a successfull device
configuration a queue is set up. Afterwards the device is reconfigured
with an invalid argument, forcing slaves to release the queues
(e.g. rte_eth_dev.data.tx_queues). Finally the failsafe's queues
are released. The queue release functions also try to release slaves'
queues using ETH(sdev)->data->tx_queues which is NULL at the time.

Add checks for NULL slaves' Tx and Rx queues before releasing them.

Fixes: a46f8d584eb8 ("net/failsafe: add fail-safe PMD")
Cc: stable@dpdk.org
Signed-off-by: Igor Romanov <igor.romanov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>