Import RFC7421_PREFIX_LENGTH from NetworkStackConstants.

RFC7421_PREFIX_LENGTH is being removed from NetworkConstants and import
it from NetworkStackConstants instead.

Bug: 290885904
Test: TH
Change-Id: I35e785be3f1a278c76b0810cad844710254b0f15

Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java

@@ -17,7 +17,8 @@
 package com.android.networkstack.tethering.apishim.api31;
 
 import static android.net.netstats.provider.NetworkStatsProvider.QUOTA_UNLIMITED;
-import static android.net.util.NetworkConstants.RFC7421_PREFIX_LENGTH;
+
+import static com.android.net.module.util.NetworkStackConstants.RFC7421_PREFIX_LENGTH;
 
 import android.net.IpPrefix;
 import android.net.MacAddress;