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-agn-rs.c b/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
index 2cdd191..ff20e50 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
@@ -2787,9 +2787,10 @@
 		repeat_rate--;
 	}
 
-	lq_cmd->agg_params.agg_frame_cnt_limit = 64;
-	lq_cmd->agg_params.agg_dis_start_th = 3;
-	lq_cmd->agg_params.agg_time_limit = cpu_to_le16(4000);
+	lq_cmd->agg_params.agg_frame_cnt_limit = LINK_QUAL_AGG_FRAME_LIMIT_MAX;
+	lq_cmd->agg_params.agg_dis_start_th = LINK_QUAL_AGG_DISABLE_START_DEF;
+	lq_cmd->agg_params.agg_time_limit =
+		cpu_to_le16(LINK_QUAL_AGG_TIME_LIMIT_DEF);
 }
 
 static void *rs_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)