Fix code problem in writePidDns

When app call startUsingNetworkFeature() to keep alive, there is a
code problem in writePidDns() to update the net.dnsX.<pid> property.

Change-Id: I83b02da4808f106c9ca00e350ad38e4bd5cba689

services/java/com/android/server/ConnectivityService.java

@@ -2158,8 +2158,9 @@ private NetworkStateTracker makeWimaxStateTracker() {
             String dnsString = dns.getHostAddress();
             if (changed || !dnsString.equals(SystemProperties.get("net.dns" + j + "." + pid))) {
                 changed = true;
-                SystemProperties.set("net.dns" + j++ + "." + pid, dns.getHostAddress());
+                SystemProperties.set("net.dns" + j + "." + pid, dns.getHostAddress());
             }
+            j++;
         }
         return changed;
     }