ice: Add slow path offload stats on port representor in switchdev

Implement callbacks to check for stats and fetch port representor stats.
Stats are taken from RX/TX ring corresponding to port representor and show
the number of bytes/packets that were not offloaded.

To see slow path stats run:
ifstat -x cpu_hits -a

Signed-off-by: Marcin Szycik <marcin.szycik@linux.intel.com>
Tested-by: Sandeep Penigalapati <sandeep.penigalapati@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>