The driver updates Tx status ring HW tail only after it finishes
processing the whole status ring, while the HW is still transmitting
from other transmit rings. This can cause back-pressure on HW if
no status entries are available.

Update HW tail of Tx status ring without waiting for the end of the
processing to help feeding back the HW with status entries and to allow
additional packet transmission.
Signed-off-by: Ahmad Masri <amasri@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>