add new fields to smb_vol to track the requested security flavor

We have this to some degree already in secFlgs, but those get "or'ed" so
there's no way to know what the last option requested was. Add new fields
that will eventually supercede the secFlgs field in the cifs_ses.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>