wlcore: workaround start_sta problem in wl12xx fw

for some reason, the wl12xx fw is not able to rx/tx
on the first start_sta cmd.
Workaround it by issuing a dummy start_sta + stop_sta
before starting the sta for the final time.

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