Restore some assignments of ti2 that were removed in the proto_tree_add_subtree[_format] conversion

bug:10270
Change-Id: I40062065add1c6a08bdabc9dcbbe53afaafca035
Reviewed-on: https://code.wireshark.org/review/2997
Reviewed-by: Anders Broman <a.broman58@gmail.com>