CIFS: SMBD: Upper layer destroys SMB Direct session on shutdown or umount

When upper layer wants to umount, make it call shutdown on transport when
SMB Direct is used.

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