iscsi-target: nullify session in failed login sequence

In case login sequence failed, make sure conn->sess is
NULL before calling wait_conn as some transports (iser)
may rely on that (waiting for session commands).
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target_login.c

@@ -1159,6 +1159,7 @@ void iscsi_target_login_sess_out(struct iscsi_conn *conn,
 	}
 	kfree(conn->sess->sess_ops);
 	kfree(conn->sess);
+	conn->sess = NULL;
 
 old_sess_out:
 	iscsi_stop_login_thread_timer(np);