refine service destroy

src/main/scala/com/github/shadowsocks/ShadowVpnService.scala

@@ -372,15 +372,14 @@ class ShadowVpnService extends VpnService {
   }
 
   def destroy() {
+    killProcesses()
+
     changeState(State.STOPPED)
     EasyTracker.getTracker.sendEvent(TAG, "stop", getVersionName, 0L)
     if (receiver != null) {
       unregisterReceiver(receiver)
       receiver = null
     }
-    spawn {
-      killProcesses()
-    }
     if (conn != null) {
       conn.close()
       conn = null

src/main/scala/com/github/shadowsocks/ShadowsocksService.scala

@@ -443,15 +443,14 @@ class ShadowsocksService extends Service {
     }
 
     // reset NAT
-    Utils.runRootCommand(Utils.getIptables + " -t nat -F OUTPUT")
-    spawn {
-      killProcesses()
-    }
+    killProcesses()
 
     super.onDestroy()
   }
 
   def killProcesses() {
+    Utils.runRootCommand(Utils.getIptables + " -t nat -F OUTPUT")
+
     val sb = new StringBuilder
 
     sb ++= "kill -9 `cat /data/data/com.github.shadowsocks/redsocks.pid`" ++= "\n"