IB/iser: Centralize iser completion contexts

Introduce iser_comp which centralizes all iser completion related
items and is referenced by iser_device and each ib_conn.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

diff --cc drivers/infiniband/ulp/iser/iscsi_iser.h
Simple merge

diff --cc drivers/infiniband/ulp/iser/iser_verbs.c
Simple merge