Target/iser: Fix initiator_depth and responder_resources

The iser target is the RDMA requester and the iser initiator is the
RDMA responder. In order to determine the max inflight RDMA READ requests
to set on the QP (initiator_depth), it should take the min between the
initiator published initiator_depth and the max inflight rdma read
requests its local HCA support (max_qp_init_rd_atom).

The target will never handle incoming RDMA READ requests so no need to
set responder_resources.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>