ixgbe: Refactor transmit map and cleanup routines

This patch implements a partial refactor of the TX map/queue and cleanup
routines.  It merges the map and queue functionality and as a result
improves the transmit performance by avoiding unnecessary reads from memory.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>