Initialize the NetworkStack before WiFi

The NetworkStack needs to be marked as start requested before any client
can use it from the system server, so it knows to queue requests until
it actually comes up.

This fixes a bug introduced in commit:
I93315ad31925bd436e21d1eabb21d5967e6aae60
where a client trying to use the network stack in the system server
before ActivityManager.systemReady() could block and eventually timeout,
resulting in a null INetworkStackConnector.

Test: booted, WiFi working
Bug: 128620654

Change-Id: Ieca2657373eba78195b387fb266fa0424fce8ada