iwlwifi: mvm: update SMPS when BT gets active

When BT traffic load gets higher, we want to avoid using the
shared antenna. In order to do so, we need to tell the AP
that we don't support MIMO any more, or at least not all
the time: in short, use the SMPS to achieve this.

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