cifs:smbd Use the correct DMA direction when sending data

When sending data, use the DMA_TO_DEVICE to map buffers. Also log the number
of requests in a compounding request from upper layer.

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