commit f01b9f73 upstream.

This patch changes isert_reg_rdma_frwr() to not use FRMR for single
dma entry requests from small I/Os, in order to avoid the associated
memory registration overhead.

Using DMA MR is sufficient here for the single dma entry requests,
and addresses a >= v3.12 performance regression.
Signed-off-by: Vu Pham <vu@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>