lib-average: Make config option selectable

Make CONFIG_AVERAGE selectable for out-of-tree users
such as compat-wireless.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

lib/Kconfig

@@ -217,6 +217,13 @@ config LRU_CACHE
 	tristate
 
 config AVERAGE
-	bool
+	bool "Averaging functions"
+	help
+	  This option is provided for the case where no in-kernel-tree
+	  modules require averaging functions, but a module built outside
+	  the kernel tree does. Such modules that use library averaging
+	  functions require Y here.
+
+	  If unsure, say N.
 
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