Quit NetworkMonitors at end of life.

We were creating and orphaning a thread for each network.
Cleanup after ourselves.

bug:16119890
Change-Id: I8c8a9fe471e43f31f712844915992084074e8047

services/core/java/com/android/server/connectivity/NetworkMonitor.java

@@ -249,8 +249,8 @@ public class NetworkMonitor extends StateMachine {
                     transitionTo(mEvaluatingState);
                     break;
                 case CMD_NETWORK_DISCONNECTED:
-                    if (DBG) log("Disconnected");
-                    transitionTo(mOfflineState);
+                    if (DBG) log("Disconnected - quitting");
+                    quit();
                     break;
                 case CMD_FORCE_REEVALUATION:
                     if (DBG) log("Forcing reevaluation");