I have an almost sorted linked list containing N distinct elements with only 1 element not in it's place. Every implementation I have seen start insertion from the beginning (unlike insertion sort on arrays) therefore the complexity will be $O(N^2)$.
Best case performance is attained when only one element is not in place. Assume the following list
You can easily show that it takes you $O(n)$ to sort via insertion sort: The inner while loop will run $n$ times when the outer loop reaches node 0. Otherwise, it will never be executed.