TetherStatsKey.java - replace U32 ifindex with S32

These are allocated in order by the kernel, if we go
over 2 billion, we've got other problems... besides
U32 to S32 conversion will work just fine anyway.

Bug: 245472520
Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I964036469fe7e0cfa77d9b062bfdbf5d2ae99bf2

common/src/com/android/net/module/util/bpf/TetherStatsKey.java

@@ -22,10 +22,10 @@ import com.android.net.module.util.Struct.Type;
 
 /** The key of BpfMap which is used for tethering stats. */
 public class TetherStatsKey extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long ifindex;  // upstream interface index
+    @Field(order = 0, type = Type.S32)
+    public final int ifindex;  // upstream interface index
 
-    public TetherStatsKey(final long ifindex) {
+    public TetherStatsKey(final int ifindex) {
         this.ifindex = ifindex;
     }
 }