iwlwifi: mvm: add a new RSS sync notification for NSSN sync

We will soon be using a new notification that will be
initiated by the driver, sent to the firmware and sent
back to all the RSS queues by the firmware. This new
notification will be useful to synchronize the NSSN across
all the queues.

For now, don't send the notification, just add the code to
handle it. Later patch will add the code to actually send
it.

While at it, validate the baid coming from the firmware to
avoid accessing an array with a bad index in the driver.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>