igc: Clean up the hw_stats structure

Remove ictxptc, ictxatc, cbtmpc, cbrdpc, cbrmpc and htcbdpc fields from
the hw_stats structure. Accordance to the i225 device
specification these fields not in use.
This patch come to clean up the driver code.

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>