iwlwifi: pcie: gen3: indicate 8k/12k RB size to device

Newer firmware versions will parse a few extra bits in the
context info to be able to determine whether we are using
bigger than 4k RBs, indicate 8k/12k to them if we actually
use those (e.g. for sniffer based on the module parameter).

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200529092401.f83f994572ca.Ibcfd66c3f9b69e68a53b3b2df8331ffb225db655@changeid