e1000: fix transmit routine exit bug

If the e1000 transmit cleanup inner loop exited early, then
cleaned might not be true.  This could cause tx hangs or other
badness.  Use count to track the total number of descriptors
cleaned instead of basing a tx queue restart off of a temporary
working state variable.

This code now makes the flow the same for e1000/e1000e/igb/ixgbe

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>