Add "total TX fail" count to "dp core stats" command output

Add "total TX fail" count to "dp core stats" command output

Warning:
This change breaks backward-compatibility of PROX socket scripting API,
because the "total TX fail" count is reported before the "last TSC"
field.
As a result, PROX scripts that make use of the "dp core stats" command,
such as the core_stats() method in helper-scripts/openstackrapid/prox_ctrl.py,
MUST be reworked to correctly parse the returned set of fields.

Change-Id: I3fe7f37dccee19f5f0b2719f262c6cfa7bad850f
Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>
Signed-off-by: Patrice Buriez <patrice.buriez@intel.com>