The commit below fixed this for the old firmware API only.
Since the new firmware API hasn't been released yet, this
doesn't fix anything on currently existing firmwares.
This completes:
commit 
afcee962b09842d0f4191beb4a2d08251b4c7705
Author: Eyal Shapira <eyal@wizery.com>
Date:   Mon Feb 9 15:18:17 2015 +0200
    iwlwifi: mvm: fix BT coex shared antenna activity check
type=bugfix
bug=not-tracked
fixes=unknown
Reviewed-by: Eyal Shapira <eyal@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
 
        if (!(mvm->fw->ucode_capa.api[0] & IWL_UCODE_TLV_API_BT_COEX_SPLIT))
                return iwl_mvm_bt_coex_is_shared_ant_avail_old(mvm);
 
-       return le32_to_cpu(mvm->last_bt_notif.bt_activity_grading) == BT_OFF;
+       return le32_to_cpu(mvm->last_bt_notif.bt_activity_grading) < BT_HIGH_TRAFFIC;
 }
 
 bool iwl_mvm_bt_coex_is_tpc_allowed(struct iwl_mvm *mvm,