iwlwifi: stats: add new api fields for statistics cmd/ntfy

The new API uses TLV format for statistics to enable fast changes
and debug on the fly.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201008181047.a45fd1a34a39.I7709305a6dc7b88d0c5119b12c9251fa6c740262@changeid