input: Write a python function to sort a linked list in ascending order.
  assert sort_linked_list([3, 1, 4, 2]) == [1, 2, 3, 4]
  assert sort_linked_list([10, 5, 8, 2, 6]) == [2, 5, 6, 8, 10]
  assert sort_linked_list([1, 2, 3]) == [1, 2, 3]
output: def sort_linked_list(lst):
      if not lst:
          return []
      return sorted(lst)