idz: Generalize msg00AD

The purpose of this request is unknown, but its message code
changed in idz2.

src/idz/userdb/decoder/unknownA.ts

@@ -0,0 +1,8 @@
+import { UnknownRequestA } from "../request/unknownA";
+
+unknownA.msgCode = 0x00ad;
+unknownA.msgLen = 0x0620;
+
+export function unknownA(buf: Buffer): UnknownRequestA {
+  return { type: "unknown_A_req" };
+}