Add "struct smb_request" Hi!

Attached find a patch that reduces access to the global
inbuf a tiny bit. It adds 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.

The second patch builds upon this and removes
get_current_mid(), another function that accesses the global
inbuf.

Commit?

Volker
