net: Fix issue with netdev_tx_reset_queue not resetting queue from XOFF state

We are seeing dev_watchdog hangs on several drivers.  I suspect this is due
to the __QUEUE_STATE_STACK_XOFF bit being set prior to a reset for link
change, and then not being cleared by netdev_tx_reset_queue.  This change
corrects that.

In addition we were seeing dev_watchdog hangs on igb after running the
ethtool tests.  We found this to be due to the fact that the ethtool test
runs the same logic as ndo_start_xmit, but we were never clearing the XOFF
flag since the loopback test in ethtool does not do byte queue accounting.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Stephen Ko <stephen.s.ko@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>