[FIX]Automatically change type when changing sale flow to drop shipping ...

Hi,

When we change sale flow to Drop shipping on SOL it doesn't change type(Procurement method) to make to order which breaks drop shipping flow.

Steps to reproduce bug:
1. Open/Create any product type product and set Procurement Method:Make to Stock
2. Set supplier and do not mark drop shipping
3. Create SO(Sale order)
4. Add product from step one.
5. Change sale flow to drop shipping
6. Confirm Sale order
7. Run Procurement Scheduler

This commit fixes the bug