iscsi/iser-target: Fix isert_conn->state hung shutdown issues

This patch addresses a couple of different hug shutdown issues
related to wait_event() + isert_conn->state.  First, it changes
isert_conn->conn_wait + isert_conn->conn_wait_comp_err from
waitqueues to completions, and sets ISER_CONN_TERMINATING from
within isert_disconnect_work().

Second, it splits isert_free_conn() into isert_wait_conn() that
is called earlier in iscsit_close_connection() to ensure that
all outstanding commands have completed before continuing.

Finally, it breaks isert_cq_comp_err() into seperate TX / RX
related code, and adds logic in isert_cq_rx_comp_err() to wait
for outstanding commands to complete before setting ISER_CONN_DOWN
and calling complete(&isert_conn->conn_wait_comp_err).

Acked-by: Sagi Grimberg <sagig@mellanox.com>
Cc: Or Gerlitz <ogerlitz@mellanox.com>
Cc: <stable@vger.kernel.org> #3.10+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/infiniband/ulp/isert/ib_isert.h

@@ -116,8 +116,8 @@ struct isert_conn {
 	struct isert_device	*conn_device;
 	struct work_struct	conn_logout_work;
 	struct mutex		conn_mutex;
-	wait_queue_head_t	conn_wait;
-	wait_queue_head_t	conn_wait_comp_err;
+	struct completion	conn_wait;
+	struct completion	conn_wait_comp_err;
 	struct kref		conn_kref;
 	struct list_head	conn_fr_pool;
 	int			conn_fr_pool_size;