Get server call tags right

include/grpc++/server.h

@@ -114,6 +114,7 @@ class Server GRPC_FINAL : public GrpcLibrary, private CallHook {
     ServerContext* const context_;
     ServerAsyncStreamingInterface* const stream_;
     CompletionQueue* const call_cq_;
+    void* const tag_;
     grpc_call* call_;
     grpc_metadata_array initial_metadata_array_;
   };

src/cpp/server/server.cc

@@ -427,6 +427,7 @@ Server::BaseAsyncRequest::BaseAsyncRequest(
       context_(context),
       stream_(stream),
       call_cq_(call_cq),
+      tag_(tag),
       call_(nullptr) {
   memset(&initial_metadata_array_, 0, sizeof(initial_metadata_array_));
 }
@@ -451,6 +452,7 @@ bool Server::BaseAsyncRequest::FinalizeResult(void** tag, bool* status) {
   }
   // just the pointers inside call are copied here
   stream_->BindCall(&call);
+  *tag = tag_;
   delete this;
   return true;
 }