iwlwifi: add value and range define for link quality command

Instead of hardcoding the link quality parameters inside the functions,
adding #define in iwl-commands.h to shared by different functions.
Also include the valid range for number of link quality parameters.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-sta.c b/drivers/net/wireless/iwlwifi/iwl-sta.c
index 5ea3bc7..2addf73 100644
--- a/drivers/net/wireless/iwlwifi/iwl-sta.c
+++ b/drivers/net/wireless/iwlwifi/iwl-sta.c
@@ -985,8 +985,9 @@
 	link_cmd.general_params.single_stream_ant_msk =
 				first_antenna(priv->hw_params.valid_tx_ant);
 	link_cmd.general_params.dual_stream_ant_msk = 3;
-	link_cmd.agg_params.agg_dis_start_th = 3;
-	link_cmd.agg_params.agg_time_limit = cpu_to_le16(4000);
+	link_cmd.agg_params.agg_dis_start_th = LINK_QUAL_AGG_DISABLE_START_DEF;
+	link_cmd.agg_params.agg_time_limit =
+		cpu_to_le16(LINK_QUAL_AGG_TIME_LIMIT_DEF);
 
 	/* Update the rate scaling for control frame Tx to AP */
 	link_cmd.sta_id = is_ap ? IWL_AP_ID : priv->hw_params.bcast_sta_id;