nvme-rdma: fix possible use-after-free in connect error flow

When start_queue fails, we need to make sure to drain the
queue cq before freeing the rdma resources because we might
still race with the completion path. Have start_queue() error
path safely stop the queue.

--
[30371.808111] nvme nvme1: Failed reconnect attempt 11
[30371.808113] nvme nvme1: Reconnecting in 10 seconds...
[...]
[30382.069315] nvme nvme1: creating 4 I/O queues.
[30382.257058] nvme nvme1: Connect Invalid SQE Parameter, qid 4
[30382.257061] nvme nvme1: failed to connect queue: 4 ret=386
[30382.305001] BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
[30382.305022] IP: qedr_poll_cq+0x8a3/0x1170 [qedr]
[30382.305028] PGD 0 P4D 0
[30382.305037] Oops: 0000 [#1] SMP PTI
[...]
[30382.305153] Call Trace:
[30382.305166]  ? __switch_to_asm+0x34/0x70
[30382.305187]  __ib_process_cq+0x56/0xd0 [ib_core]
[30382.305201]  ib_poll_handler+0x26/0x70 [ib_core]
[30382.305213]  irq_poll_softirq+0x88/0x110
[30382.305223]  ? sort_range+0x20/0x20
[30382.305232]  __do_softirq+0xde/0x2c6
[30382.305241]  ? sort_range+0x20/0x20
[30382.305249]  run_ksoftirqd+0x1c/0x60
[30382.305258]  smpboot_thread_fn+0xef/0x160
[30382.305265]  kthread+0x113/0x130
[30382.305273]  ? kthread_create_worker_on_cpu+0x50/0x50
[30382.305281]  ret_from_fork+0x35/0x40
--

Reported-by: Nicolas Morey-Chaisemartin <NMoreyChaisemartin@suse.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>