Enforce permission check in getUidStats function

The NetworkStatsService.getUidStats() currently doesn't have any
permission check to make sure unpriviledged apps cannot read the stats
of a different uid. It will protentially have security problem since
apps with ACCESS_NETWORK_STATS permission can directly calling into
NetworkStatsService and bypass the check in TrafficStats. Move the uid
check from TrafficStats to NetworkStatsService to fix the problem.

Bug: 129151407
Test: atest AppSecurityTests#testAppFailAccessPrivateData_full
Test: atest AppSecurityTests#testAppFailAccessPrivateData_instant
Test: atest android.app.usage.cts.NetworkUsageStatsTest
Test: atest NetworkStatsBinderTest

Change-Id: Iae85676cfe5f114da69ec278afc2c904bc907234