MB-7502 Fix inner node callbacks for walk API

I accidentally killed this code in a merge, and it broke
couch_dbdump's --tree option.

Change-Id: I549bd8d4ee141775b5a821889a68bfe66092867e
Reviewed-on: http://review.couchbase.org/23769
Reviewed-by: Fulu Li <fulu@couchbase.com>
Tested-by: Fulu Li <fulu@couchbase.com>