Fix NetworkOnMainThreadException caused by dnsjava

refresh().

java.lang.ExceptionInInitializerError
at org.jivesoftware.smack.SmackAndroid$1.onReceive(SmackAndroid.java:26)
at android.app.LoadedApk$ReceiverDispatcher$Args.run(LoadedApk.java:763)
at android.os.Handler.handleCallback(Handler.java:725)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5306)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
at dalvik.system.NativeStart.main(Native Method)
Caused by: android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1128)
at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
at java.net.InetAddress.getByName(InetAddress.java:289)
at org.xbill.DNS.SimpleResolver.<init>(SimpleResolver.java:56)
at org.xbill.DNS.SimpleResolver.<init>(SimpleResolver.java:68)
at org.xbill.DNS.ExtendedResolver.<init>(ExtendedResolver.java:266)
at org.xbill.DNS.Lookup.refreshDefault(Lookup.java:86)
at org.xbill.DNS.Lookup.<clinit>(Lookup.java:97)
... 11 more