libhardware_legacy: Add support for oneshot WiFi setup

 * For a certain device, we need to wait for the RIL to dump out
   the NV items which contain the WiFi MAC address. This is
   done by starting a service and waiting for it to set a property
   indicating completion. The existing module loader already works
   like this, so we can just use that.
 * Reorder the ifdefs so this works when the driver is not built
   as a module.

Change-Id: Ic69dd5c1087122b3b7d939a8647785bf97b95a0c