Fix address bug in Shippit integration (Australia)

Currently the Address 'State' field in DEAR and DEAR B2B is a text menu, allowing you to enter anything, and it does not verify if correct.

This causes issues when receiving shipping rates from Shippit.

Some rates (particularly eParcel and eParcel Express) are only retrieved if State CODES are entered in the field (such as WA, SA, QLD) are used, and will not display if State NAME is entered any other way (Such as Western Australia).

This is a particular issue for B2B customers who may enter anything in the field, and not always get the shipping options and prices that they should.