luci-app-statistics: improve scaling of the associated stations graph

Improve scaling of the associated stations graph on the wireless page.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>
(cherry picked from commit dccf485922)

applications/luci-app-statistics/luasrc/statistics/rrdtool/definitions/iwinfo.lua

@@ -74,6 +74,8 @@ function rrdargs( graph, plugin, plugin_instance )
 	local stations = {
 		title = "%H: Associated stations on %pi",
 		vlabel = "Stations",
+		y_min = "0",
+		alt_autoscale_max = true,
 		number_format = "%3.0lf",
 		data = {
 			types = { "stations" },