Bug 900450 - Reset UDP socket to allow re-initialization. r=dougt

dom/push/src/PushService.jsm

@@ -295,6 +295,8 @@ this.PushService = {
         // online, it is likely that these statements will be no-ops.
         if (this._udpServer) {
           this._udpServer.close();
+          // Set to null since this is checked in _listenForUDPWakeup()
+          this._udpServer = null;
         }
 
         this._shutdownWS();
@@ -504,6 +506,7 @@ this.PushService = {
 
     if (this._udpServer) {
       this._udpServer.close();
+      this._udpServer = null;
     }
 
     // All pending requests (ideally none) are dropped at this point. We