BpfHandler.h - switch mStatsMapB from BpfMap to BpfMapRO

We'd like to switch more of these, but this is the only one
where tests don't get in our way.

We'll fix the rest later.  This gives us an *example* for
further testing.

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I9b280c7ba2d19644fc3cdd0c132de85f45df69b4

netd/BpfHandler.cpp

@@ -199,6 +199,7 @@ int BpfHandler::tagSocket(int sockFd, uint32_t tag, uid_t chargeUid, uid_t realU
 
     BpfMap<StatsKey, StatsValue>& currentMap =
             (configuration.value() == SELECT_MAP_A) ? mStatsMapA : mStatsMapB;
+    // HACK: mStatsMapB becomes RW BpfMap here, but countUidStatsEntries doesn't modify so it works
     base::Result<void> res = currentMap.iterate(countUidStatsEntries);
     if (!res.ok()) {
         ALOGE("Failed to count the stats entry in map %d: %s", currentMap.getMap().get(),