r23724: Reduce access to the global inbuf a tiny bit. Add a struct smb_request

r23724: Reduce access to the global inbuf a tiny bit. Add a struct smb_request
that contains some of the fields from the SMB header, removing the need
to access inbuf directly. This right now is used only in the open file
code & friends, and creating that header is only done when needed. This
needs more work, but it is a start.

Jeremy, I'm only checking this into 3_0, please review before I merge it
to _26.

Volker
(This used to be commit ca988f4e79e977160d82e86486972afd15d4acf5)