iwlwifi: mvm: don't send SMPS action frame with single RX antenna

Products that have only 1 antenna in Rx don't support MIMO
in RX. As a consequence, they will be in STATIC always.
Don't tell mac80211 to update SMPS in that case. mac80211
would send an action frame to the AP which is clearly
bogus.
As a matter of fact, we have seen that some APs send a
deauth when that happens.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>