CIFS: SMBD: Add SMB Direct protocol initial values and constants

To prepare for protocol implementation, add constants and user-configurable
values for the SMB Direct protocol.

Signed-off-by: Long Li <longli@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Acked-by: Ronnie Sahlberg <lsahlber.redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>