net: airoha: Take into account out-of-order tx completions in airoha_dev_xmit()

Completion napi can free out-of-order tx descriptors if hw QoS is
enabled and packets with different priority are queued to same DMA ring.
Take into account possible out-of-order reports checking if the tx queue
is full using circular buffer head/tail pointer instead of the number of
queued packets.

Fixes: 23020f04 ("net: airoha: Introduce ethernet support for EN7581 SoC")
Suggested-by: Simon Horman <horms@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251012-airoha-tx-busy-queue-v2-1-a600b08bab2d@kernel.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>