airo: Invoke airo_read_wireless_stats() directly

airo_get_wireless_stats() is the iw_handler_if::get_wireless_stats()
callback of this driver. This callback was not allowed to sleep until
commit a160ee69 ("wext: let get_wireless_stats() sleep") in v2.6.32.

airo still delegates the readout to a thread, which is not longer
necessary.

Invoke airo_read_wireless_stats() directly from the callback and remove
the now unused JOB_WSTATS handling.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: linux-wireless@vger.kernel.org
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201101211536.2966644-3-bigeasy@linutronix.de