Tx ring buffers after tx_ring->next_to_use are volatile and could
change, possibly causing a crash.  Stop cleaning when we hit
tx_ring->next_to_use.
Signed-off-by: Terry Loftin <terry.loftin@hp.com>
Acked-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>