[ST02.1] Add TYPE_CNAME constant to DnsResolver

This would be needed for subsequent patches that synthesizing DNS
packets for testing purpose.

Bug: 139774492
Test: atest DnsPacketTest DnsResolverTest
Change-Id: I5e58f99b09b693f167178e56f008be8b42d9417a
diff --git a/framework/api/current.txt b/framework/api/current.txt
index 547b7e2..09b4538 100644
--- a/framework/api/current.txt
+++ b/framework/api/current.txt
@@ -188,6 +188,7 @@
     field public static final int FLAG_NO_RETRY = 1; // 0x1
     field public static final int TYPE_A = 1; // 0x1
     field public static final int TYPE_AAAA = 28; // 0x1c
+    field public static final int TYPE_CNAME = 5; // 0x5
   }
 
   public static interface DnsResolver.Callback<T> {