rpc: fix a virObject typo error in struct _virNetServer

This typo will crash libvirtd when it recevies signal SIGINT

src/rpc/virnetserver.c

@@ -64,7 +64,7 @@ struct _virNetServerJob {
 };
 
 struct _virNetServer {
-    virObjectPtr object;
+    virObject object;
 
     virMutex lock;