Reference DataSaver setting from BPF map on V+ only

Only reference DataSaverEnabled map on V+ platform because the
information in map before platform V is not time-precise. See comment in
this commit for detail.

Bug: 288340533
Test: presubmit
Change-Id: I0795e88e6006e6d24d27b63c31d0e3ed81d0262c

DnsResolver/DnsBpfHelper.cpp

@@ -62,8 +62,13 @@ base::Result<bool> DnsBpfHelper::isUidNetworkingBlocked(uid_t uid, bool metered)
   if (isBlockedByUidRules(enabledRules.value(), uidRules)) return true;
 
   // For data saver.
-  if (!metered) return false;
-
+  // DataSaverEnabled map on V+ platforms is the only reliable source of information about the
+  // current data saver status. While ConnectivityService offers two ways to update this map for U
+  // and V+, the U- platform implementation can have delays, potentially leading to inaccurate
+  // results. Conversely, the V+ platform implementation is synchronized with the actual data saver
+  // state, making it a trustworthy source. Since this library primarily serves DNS resolvers,
+  // relying solely on V+ data prevents erroneous blocking of DNS queries.
+  if (android::modules::sdklevel::IsAtLeastV() && metered) {
     // The background data setting (PENALTY_BOX_MATCH) and unrestricted data usage setting
     // (HAPPY_BOX_MATCH) for individual apps override the system wide Data Saver setting.
     if (uidRules & PENALTY_BOX_MATCH) return true;
@@ -74,5 +79,8 @@ base::Result<bool> DnsBpfHelper::isUidNetworkingBlocked(uid_t uid, bool metered)
     return dataSaverSetting.value();
   }
 
+  return false;
+}
+
 }  // namespace net
 }  // namespace android