Add domain prefetch, fix ping issue

package/luci/files/luci/i18n/smartdns.zh-cn.po

@@ -67,6 +67,12 @@ msgstr "双栈IP优选"
 msgid "Enable IP selection between IPV4 and IPV6"
 msgstr "启用或禁用IPV4，IPV6间的IP优选策略。"
 
+msgid "Domain prefetch"
+msgstr "域名预加载"
+
+msgid "Enable domain prefetch, accelerate domain response speed."
+msgstr "启用域名预加载，加速域名响应速度。"
+
 msgid "Redirect"
 msgstr "重定向"
 

package/luci/files/luci/model/cbi/smartdns/smartdns.lua

@@ -60,6 +60,14 @@ o.cfgvalue    = function(...)
     return Flag.cfgvalue(...) or "0"
 end
 
+---- Domain prefetch load 
+o = s:taboption("settings", Flag, "prefetch_domain", translate("Domain prefetch"), translate("Enable domain prefetch, accelerate domain response speed."))
+o.rmempty     = false
+o.default     = o.disabled
+o.cfgvalue    = function(...)
+    return Flag.cfgvalue(...) or "0"
+end
+
 ---- Redirect
 o = s:taboption("settings", ListValue, "redirect", translate("Redirect"), translate("SmartDNS redirect mode"))
 o.placeholder = "none"