Update the logic of isFeatureEnabled and isFeatureNotChickenedOut

If the flag value is unset or 0, isFeatureEnabled return false and
isFeatureNotChickenedOut return true.
If the flag value is -1 (force disable), both return false.
If the flag value is other values, both query the package version and
return `flagValue <= packageVersion`

Now the only difference is a default behavior when the flag is not set
or 0.
So isFeatureEnabled and isFeatureNotChickenedOut can use the same flag.

This CL also fixes the issue in rollback.
Before this CL, isFeatureNotChickenedOut did not check the module
version and could have a issue if there is a rollback.

Test: NetworkStaticLibsTests
Bug: 279108992
Change-Id: I12d6ebadff3aee7b7c614aca4eb0a34ef0db9857

service/src/com/android/server/BpfNetMaps.java

@@ -254,7 +254,7 @@ public class BpfNetMaps {
         if (sInitialized) return;
         if (sEnableJavaBpfMap == null) {
             sEnableJavaBpfMap = SdkLevel.isAtLeastU() ||
-                    DeviceConfigUtils.isTetheringFeatureNotChickenedOut(
+                    DeviceConfigUtils.isTetheringFeatureNotChickenedOut(context,
                             BPF_NET_MAPS_FORCE_DISABLE_JAVA_BPF_MAP);
         }
         Log.d(TAG, "BpfNetMaps is initialized with sEnableJavaBpfMap=" + sEnableJavaBpfMap);