Before:
  let g:vim_markdown_new_list_item_indent = 2

After:
  unlet g:vim_markdown_new_list_item_indent

Given markdown;
* item1

Do (new line from the first item of the list and add the second item):
  o* item2

Expect (insert 2 spaces to the head of second item):
  * item1
    * item2