Clear Calling UID if calling reportBootstrapAtom from system server

StatsBootstrap will verify if the host uid
is the same in the packed atom and when got
using Binder.getCallingUid.

Clearing Calling Identity for local binder
calls ensures that any call made from
system_server has AID_SYSTEM as its uid.

Test: atest binderStatsPusherUnitTest
Bug: 299356196
Flag: build.RELEASE_LIBBINDER_BINDER_OBSERVER
Change-Id: I6a2a0f61db4c4bed70bfaeeeb79c497562da3387