AP interfaces still use some static TX queues (for probes,
broadcast and multicast frames). These queues were not stopped
correctly when the transport layer indicated the queue should be
stopped. As a result, when flushing the queues, new frames from
the overflow queue were tx'd, so the queues still had frames after
flushing. This ended up in an assert since trying to remove a station
with non-empty queues.

Fix it by stopping the static queues correctly when required.
Signed-off-by: Avraham Stern <avraham.stern@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>