mac80211: minstrel_ht: fix issue in calculating success probability

Missing braces in a macro were leading to badly working rates sometimes
getting a success probabilty of 1.0

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/kernel/mac80211/patches/subsys/353-mac80211-minstrel_ht-fix-MINSTREL_FRAC-macro.patch

@@ -0,0 +1,21 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Wed, 28 Apr 2021 21:03:13 +0200
+Subject: [PATCH] mac80211: minstrel_ht: fix MINSTREL_FRAC macro
+
+Add missing braces to avoid issues with e.g. using additions in the
+div expression
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/rc80211_minstrel_ht.h
++++ b/net/mac80211/rc80211_minstrel_ht.h
+@@ -14,7 +14,7 @@
+
+ /* scaled fraction values */
+ #define MINSTREL_SCALE  12
+-#define MINSTREL_FRAC(val, div) (((val) << MINSTREL_SCALE) / div)
++#define MINSTREL_FRAC(val, div) (((val) << MINSTREL_SCALE) / (div))
+ #define MINSTREL_TRUNC(val) ((val) >> MINSTREL_SCALE)
+
+ #define EWMA_LEVEL	96	/* ewma weighting factor [/EWMA_DIV] */