cifs: add a smb_version_operations/values structures and a smb_version enum

We need a way to dispatch different operations for different versions.
Behold the smb_version_operations/values structures. For now, those
structures just hold the version enum value and nothing uses them.
Eventually, we'll expand them to cover other operations/values as we
change the callers to dispatch from here.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>