iwlwifi: fix rate-scaling algorithm for BT combo devices

iwlwifi tries to avoid using antenna B in BT combo devices when BT
is active. A bug in the rate-scaling algorithm was causing the combo
device to never attempt MIMO rates. Fix the algorithm to
opportunistically try MIMO rates when BT traffic is low.
Signed-off-by: Meenakshi Venkataraman <meenakshi.venkataraman@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-agn-rs.c

@@ -1458,10 +1458,8 @@ static int rs_move_legacy_other(struct iwl_priv *priv,
 		break;
 	case IWL_BT_COEX_TRAFFIC_LOAD_LOW:
 		/* avoid antenna B unless MIMO */
-		valid_tx_ant =
-			first_antenna(hw_params(priv).valid_tx_ant);
 		if (tbl->action == IWL_LEGACY_SWITCH_ANTENNA2)
-			tbl->action = IWL_LEGACY_SWITCH_ANTENNA1;
+			tbl->action = IWL_LEGACY_SWITCH_SISO;
 		break;
 	case IWL_BT_COEX_TRAFFIC_LOAD_HIGH:
 	case IWL_BT_COEX_TRAFFIC_LOAD_CONTINUOUS:
@@ -1636,10 +1634,8 @@ static int rs_move_siso_to_other(struct iwl_priv *priv,
 		break;
 	case IWL_BT_COEX_TRAFFIC_LOAD_LOW:
 		/* avoid antenna B unless MIMO */
-		valid_tx_ant =
-			first_antenna(hw_params(priv).valid_tx_ant);
 		if (tbl->action == IWL_SISO_SWITCH_ANTENNA2)
-			tbl->action = IWL_SISO_SWITCH_ANTENNA1;
+			tbl->action = IWL_SISO_SWITCH_MIMO2_AB;
 		break;
 	case IWL_BT_COEX_TRAFFIC_LOAD_HIGH:
 	case IWL_BT_COEX_TRAFFIC_LOAD_CONTINUOUS: