Allow grilservice apps to access app_api_service

Sync solution from ag/12369854 which allow grilservice_app to use
app_api_service.
The tethering_service is one kind of app_api_service.
The activity_service is also one kind of app_api_service.

Log from b/168419215
auditd  : avc:  denied  { find } for pid=17254 uid=10116 name=tethering scontext=u:r:grilservice_app:s0:c116,c256,c512,c768 tcontext=u:object_r:tethering_service:s0 tclass=service_manager permissive=0

Bug: 169057554
Test: the device can boot to home. check if avc denied from grilservice_app.
Change-Id: Id6eeea8c8cf4ac5866a98b2459a8f6911200c14d
diff --git a/vendor/google/grilservice_app.te b/vendor/google/grilservice_app.te
index ef2430f..1d1ff57 100644
--- a/vendor/google/grilservice_app.te
+++ b/vendor/google/grilservice_app.te
@@ -4,6 +4,6 @@
 
 allow grilservice_app hal_radioext_hwservice:hwservice_manager find;
 allow grilservice_app hal_wifi_ext_hwservice:hwservice_manager find;
-allow grilservice_app activity_service:service_manager find;
+allow grilservice_app app_api_service:service_manager find;
 binder_call(grilservice_app, hal_radioext_default)
 binder_call(grilservice_app, hal_wifi_ext)