txqs_lock is interfering with wake_tx_queue submitting more frames.
so queues don't get filled in and don't keep firmware/hardware busy
enough. This change helps to reduce the txqs_lock contention and
wake_tx_queue() blockage to being possible in txrx_unref().

To reduce turn around time of wake_tx_queue ops and to maintain fairness
among all txqs, the callback is updated to push first txq alone from
pending list for every wake_tx_queue call. Remaining txqs will be
processed later upon tx completion.

Below improvements are observed in push-only mode and validated on
IPQ4019 platform. With this change, in AP mode ~10Mbps increase is
observed in downlink (AP -> STA) traffic and approx. 5-10% of CPU
usage is reduced.

Major improvement is observed in 1-hop Mesh mode topology in 11ACVHT80.
Compared to Infra mode, CPU overhead is higher in Mesh mode due to path
lookup and no fast-xmit support. So reducing spin lock contention is
helping in Mesh.

             TOT       +change
           --------    --------
TCP DL     545 Mbps    595 Mbps
TCP UL     555 Mbps    585 Mbps
Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>