ixgbe: avoid HW lockup when adapter is reset with Tx work pending

This change is meant to avoid a hardware lockup when Tx work is still
pending and we request a reset.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>