Don't rematch all requests when adding new ones

With the network selection rewrite in S, rematching a single request can
now easily be done; this can be used as an optimization in
handleRegisterNetworkRequests to avoid rematching all requests when
registering a new one.

This can be disabled by a flag that is unset by default,
REMATCH_ALL_REQUESTS_ON_REGISTER.

Test: atest ConnectivityServiceTest
Change-Id: If76f79b41ac88863974f7025624667134bea2570

tests/unit/java/com/android/server/ConnectivityServiceTest.java

@@ -327,6 +327,7 @@ import com.android.net.module.util.LocationPermissionChecker;
 import com.android.server.ConnectivityService.ConnectivityDiagnosticsCallbackInfo;
 import com.android.server.ConnectivityService.NetworkRequestInfo;
 import com.android.server.ConnectivityServiceTest.ConnectivityServiceDependencies.ReportedInterfaces;
+import com.android.server.connectivity.ConnectivityFlags;
 import com.android.server.connectivity.MockableSystemProperties;
 import com.android.server.connectivity.Nat464Xlat;
 import com.android.server.connectivity.NetworkAgentInfo;
@@ -1916,6 +1917,16 @@ public class ConnectivityServiceTest {
             mReportedInterfaceHistory.add(new ReportedInterfaces(context, iface, transportTypes));
             super.reportNetworkInterfaceForTransports(context, iface, transportTypes);
         }
+
+        @Override
+        public boolean isFeatureEnabled(Context context, String name, boolean defaultEnabled) {
+            switch (name) {
+                case ConnectivityFlags.NO_REMATCH_ALL_REQUESTS_ON_REGISTER:
+                    return true;
+                default:
+                    return super.isFeatureEnabled(context, name, defaultEnabled);
+            }
+        }
     }
 
     private static void initAlarmManager(final AlarmManager am, final Handler alarmHandler) {