rdma_disconnect may be called in 2 code flows:
- isert_wait_conn: disconnect initiated be the target
- disconnected_handler: disconnect invoked by the initiator

In case isert_conn->disconnect is true then rdma_disconnect
was called in disconnected handler, no need to call it again
from isert_wait_conn.
Signed-off-by: NSagi Grimberg <sagig@mellanox.com>
Signed-off-by: NNicholas Bellinger <nab@linux-iscsi.org>