r3383: avoid multi-part SMBtrans and SMBtrans2 replies until our client library can...

r3383: avoid multi-part SMBtrans and SMBtrans2 replies until our client library can handle
them properly (they are difficult to do in an async fashion).

By choosing trans.in.max_data to fix in the negotiated buffer size a
server won't send us multi-part replies.

I notice that windows seems to avoid them too :)
(This used to be commit e23edf762cace35f937959c9ffbef718431a79b9)