iwlwifi: mvm: support Coex Schema 2

The new coex schema requires moving to SISO only when BT AG is 4.
Adjust the SISO criteria according to the coex schema version reported
by firmware.

Signed-off-by: Erel Geron <erelx.geron@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>