improve DNS utils

src/main/scala/com/github/shadowsocks/utils/DnsUtils.scala

@@ -0,0 +1,17 @@
+package com.github.shadowsocks.utils
+
+import java.net.InetAddress
+
+import android.net.{Network, ConnectivityManager}
+
+
+object DnsUtils {
+  def getDnsServers(mgr: ConnectivityManager, network: Network): java.util.List[InetAddress] = {
+    val getLinkProperties = mgr.getClass.getMethod("getLinkProperties", network.getClass)
+    getLinkProperties.invoke(mgr, network).asInstanceOf[java.util.List[InetAddress]]
+  }
+
+  def getNetId(network: Network): Int = {
+    network.getClass.getDeclaredField("netId").get(network).asInstanceOf[Int]
+  }
+}