iser-target: Fix variable-length response error completion

iser-target: Fix variable-length response error completion

[ Upstream commit 9253e667ab50fd4611a60e1cdd6a6e05a1d91cf1 ]

Since commit "2426bd456a6 target: Report correct response ..."
we might get a command with data_size that does not fit to
the number of allocated data sg elements. Given that we rely on
cmd t_data_nents which might be different than the data_size,
we sometimes receive local length error completion. The correct
approach would be to take the command data_size into account when
constructing the ib sg_list.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Jenny Falkovich <jennyf@mellanox.com>
Cc: stable@vger.kernel.org # 3.16+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>