Target/iser: Centralize ib_sig_domain setting

Later there will be more parameters to set, so we want to do it in a
centralized place.

This patch does not change any functionality.

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

diff --cc drivers/infiniband/ulp/isert/ib_isert.c
Simple merge