wlcore: don't take mutex before stopping queues

Protect all functions touching queue_stop_reasons by spin-lock, since
they are accessed by op_tx. Now there's no need to take the mutex
before caling wlcore_queue_xxx functions.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>