BpfHandler.h - switch mStatsMapB from BpfMap to BpfMapRO

We'd like to switch more of these (as netd should only be
writing into the cookie map), but this is the only one
where tests (and the BpfMap vs BpfMapRO inheritence inversion)
don't get in our way.

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

Bug: 218408035
Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I9b280c7ba2d19644fc3cdd0c132de85f45df69b4
(cherry picked from commit 21ce721bc087d679686acedd06ec7d2b19cad164)
Merged-In: I9b280c7ba2d19644fc3cdd0c132de85f45df69b4
diff --git a/netd/BpfHandler.h b/netd/BpfHandler.h
index 05b9ebc..7e3b94d 100644
--- a/netd/BpfHandler.h
+++ b/netd/BpfHandler.h
@@ -23,6 +23,7 @@
 #include "bpf_shared.h"
 
 using android::bpf::BpfMap;
+using android::bpf::BpfMapRO;
 
 namespace android {
 namespace net {
@@ -61,7 +62,7 @@
 
     BpfMap<uint64_t, UidTagValue> mCookieTagMap;
     BpfMap<StatsKey, StatsValue> mStatsMapA;
-    BpfMap<StatsKey, StatsValue> mStatsMapB;
+    BpfMapRO<StatsKey, StatsValue> mStatsMapB;
     BpfMap<uint32_t, uint32_t> mConfigurationMap;
     BpfMap<uint32_t, uint8_t> mUidPermissionMap;