Add U8 subclasses to Struct

BPF maps require classes to extend struct.
U8 is used as value of UidCounterSetMap.

Test: m
Change-Id: Ieacc6d83c9c55cbe2b4513e7e8356fbe4a7d0058
diff --git a/common/device/com/android/net/module/util/Struct.java b/common/device/com/android/net/module/util/Struct.java
index f4d4163..ac9dc54 100644
--- a/common/device/com/android/net/module/util/Struct.java
+++ b/common/device/com/android/net/module/util/Struct.java
@@ -731,6 +731,16 @@
         return sb.toString();
     }
 
+    /** A simple Struct which only contains a u8 field. */
+    public static class U8 extends Struct {
+        @Struct.Field(order = 0, type = Struct.Type.U8)
+        public final short val;
+
+        public U8(final short val) {
+            this.val = val;
+        }
+    }
+
     public static class U32 extends Struct {
         @Struct.Field(order = 0, type = Struct.Type.U32)
         public final long val;