ixgbe: add/update descriptor maps in comments

Adds/updates ASCII descriptor maps for 82598 and 82599 Tx/Rx descriptors.
Current descriptor maps were out of date for 82598 and incorrect for
82599.

Signed-off-by: Josh Hay <joshua.a.hay@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>