dns: convert plugin output to local types for instanceof checks

lib/dns/server.js

@@ -413,8 +413,9 @@ class RootServer extends DNSServer {
         this.logger.debug(e.stack);
       }
 
-      if (res)
-        return res;
+      if (res) {
+        return Message.decode(res.encode());
+      }
     }
 
     // Hit the cache first.
@@ -442,6 +443,11 @@ class RootServer extends DNSServer {
   }
 
   signRRSet(rrset, type) {
+    // Intended to be called by plugin.
+    // Not all bns `Record` instances are created equal.
+    rrset = rrset.map((record) => {
+      return Record.decode(record.encode());
+    });
     // No return value, signature is pushed to rrset.
     key.signZSK(rrset, type);
   }