mac80211: don't start new netdev queues if driver stopped

If a new netdev (e.g. an AP VLAN) is created while the driver
has queues stopped, the new netdev queues will be started even
though they shouldn't. This will lead to frames accumulating
on the internal mac80211 pending queues instead of properly
being held on the netdev queues.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>