mt76: fix tx skb error handling in mt76_dma_tx_queue_skb

stable inclusion
from stable-5.10.27
commit a9daba140178df9ad5bffd646517709086d10854
bugzilla: 51493

--------------------------------

[ Upstream commit ae064fc0 ]

When running out of room in the tx queue after calling drv->tx_prepare_skb,
the buffer list will already have been modified on MT7615 and newer drivers.
This can leak a DMA mapping and will show up as swiotlb allocation failures
on x86.

Fix this by moving the queue length check further up. This is less accurate,
since it can overestimate the needed room in the queue on MT7615 and newer,
but the difference is small enough to not matter in practice.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210216135119.23809-1-nbd@nbd.name


Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by:   Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>