traced: change guest_soc.model prop string

It's a bit easier to maintain guest_soc.model as boot time flag on the
cuttlefish side rather than ro.guest_soc.model at runtime. So look for
ro.boot.guest_soc.model instead.

Test: collected and parsed a trace with the new prop being set
Bug: 374790255
Change-Id: I880642b6c2058a4a1ee3899adfd3387efb46b8b2
Signed-off-by: David Dai <davidai@google.com>

src/tracing/service/tracing_service_impl.cc

@@ -3780,7 +3780,7 @@ void TracingServiceImpl::EmitSystemInfo(std::vector<TracePacket>* packets) {
 
   // guest_soc model is not always present
   std::string guest_soc_model_value =
-      base::GetAndroidProp("ro.guest_soc.model");
+      base::GetAndroidProp("ro.boot.guest_soc.model");
   if (!guest_soc_model_value.empty()) {
     info->set_android_guest_soc_model(guest_soc_model_value);
   }