igb: Add support for bulk Tx cleanup & cleanup boolean logic

This patch enables bulk free in Tx cleanup for igb and cleans up the
boolean logic in the polling routines for igb in the hopes of avoiding
any mix-ups similar to what occurred with i40e and i40evf.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>