[NET]: Fix locking in shaper driver.

 o use a semaphore instead of an opencoded and racy lock
 o move locking out of shaper_kick and into the callers - most just
   released the lock before calling shaper_kick
 o remove in_interrupt() tests.  from ->close we can always block, from
   ->hard_start_xmit and timer context never

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>