iwlwifi: mvm: rs: fix and cleanup rs_get_rate_action

Change the down/upscale decision logic a bit to be based
on different success ratio thresholds. This fixes the implementation
compared to the rate scale algorithm which was planned to yield
optimal results. Also fix a case where a lower rate wasn't explored
despite being a potential for better throughput.
While at it rewrite rs_get_rate_action to be more clear and clean.

Cc: <stable@vger.kernel.org> [3.14]
Signed-off-by: Eyal Shapira <eyalx.shapira@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/mvm/rs.h b/drivers/net/wireless/iwlwifi/mvm/rs.h
index 9892d92..fbb476a 100644
--- a/drivers/net/wireless/iwlwifi/mvm/rs.h
+++ b/drivers/net/wireless/iwlwifi/mvm/rs.h
@@ -156,6 +156,7 @@
 #define IWL_RATE_HIGH_TH		10880	/*  85% */
 #define IWL_RATE_INCREASE_TH		6400	/*  50% */
 #define RS_SR_FORCE_DECREASE		1920	/*  15% */
+#define RS_SR_NO_DECREASE		10880	/*  85% */
 
 #define LINK_QUAL_AGG_TIME_LIMIT_DEF	(4000) /* 4 milliseconds */
 #define LINK_QUAL_AGG_TIME_LIMIT_MAX	(8000)