i40e: Record dma buffer info for dummy packets

Save information that we can use while cleaning the tx ring. Also record
the time_stamp since we will need it to check tx hangs.

Change-Id: Ia3f1c17f6fec9bcb7fef2542d77eac7f6c4f115c
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>