Merge changes from topic "bpfmap1"

* changes:
  netd.c - reduce privs on maps
  BpfHandler.h - switch mStatsMapB from BpfMap to BpfMapRO
  BpfNetworkStatsTest - cleanup
  TEST_BPF_MAP -> BPF_MAP_MAKE_VISIBLE_FOR_TESTING
  BpfHandlerTest - minor fixups
  TrafficController - minor cleanup