Allow the driver to wake/stop the queues for multiple reasons. A queue
is started when no stop-reasons exist.

Convert all wake/stop queue calls to use the new API.

Before, a stopped queue was almost synonymous a high-watermark on Tx.
Remove a bit of code in wl12xx_tx_reset() that relied on it.

Internal packets arriving from mac80211 are also discarded when a queue
is stopped. A notable exception to this is the watermark reason, which
is a "soft"-stop reason. We allow traffic to gradually come to a halt,
but we don't mind spurious packets here and there. This is merely a flow
regulation mechanism.

Based on a similar patch by Eliad Peller <eliadWizery.com>.
Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>