net: airoha: stop net_device TX queue before updating CPU index

net: airoha: stop net_device TX queue before updating CPU index

Currently, airoha_eth driver updates the CPU index register prior of
verifying whether the number of free descriptors has fallen below the
threshold.
Move net_device TX queue length check before updating the TX CPU index
in order to update TX CPU index even if there are more packets to be
transmitted but the net_device TX queue is going to be stopped
accounting the inflight packets.

Fixes: 1d304174106c ("net: airoha: Implement BQL support")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260421-airoha-xmit-stop-condition-v1-1-e670d6a48467@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>