gluon-core: introduce device_uses_wlan() helper

package/gluon-core/luasrc/usr/lib/lua/gluon/wireless.lua

@@ -150,6 +150,17 @@ function M.device_supports_mfp(uci)
 	return supports_mfp
 end
 
+function M.device_uses_wlan(uci)
+	local ret = false
+
+	uci:foreach('wireless', 'wifi-device', function()
+		ret = true
+		return false
+	end)
+
+	return ret
+end
+
 function M.device_uses_11a(uci)
 	local ret = false