Revert "Remove unused codes that was used in setChildChain"

This reverts commit b1144d76717e0f858e87f2bd673ce0f519234baa.

Reason for revert: We decided to have experiment and switch old code path and new code path based on a flag. So the codes removed by this CL is needed.

Bug: 217624062
Test: m

Change-Id: Icb8a353a74935ed97f8e102ba54020825676b817
diff --git a/service/src/com/android/server/BpfNetMaps.java b/service/src/com/android/server/BpfNetMaps.java
index 3befd86..0270fc2 100644
--- a/service/src/com/android/server/BpfNetMaps.java
+++ b/service/src/com/android/server/BpfNetMaps.java
@@ -637,6 +637,7 @@
     private native int native_addNiceApp(int uid);
     @GuardedBy("sUidOwnerMap")
     private native int native_removeNiceApp(int uid);
+    private native int native_setChildChain(int childChain, boolean enable);
     @GuardedBy("sUidOwnerMap")
     private native int native_replaceUidChain(String name, boolean isAllowlist, int[] uids);
     @GuardedBy("sUidOwnerMap")