ixgbe: Clear out stray tx work on link down

Ayyappan at VMware noticed that we're missing this check from ixgbe which
is in our other drivers.  The difference with this implementation from our
other drivers is that this checks all the tx queues rather than just tx[0].

Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>