Variable dictionary format - support Starent
I already see that there was a request to support starent #30 . Unfortunately this vendor changed the spec and introduced 2 byte size of VSA Type and Length fields.

Previous request was not complete and I tried to make a fully scalable solution where we can support different sizes.
This is defined in dictionary and same practices is used by freeradius also.
I was careful to only edit logic regarding vendor specific attributes and this change should not affect default packets. Maybe now some public methods can be deleted but I did not want to remove any public methods in order not to break the API.
Could you rebase with "master" so the CI is triggered for this PR? Thanks.
Branch is now rebased with master
Thanks. Does this change warrant a bump in major/minor version?