Bluetooth: Host: Fix unable cleanup conn

The peripheral is configured to update the connection
parameters for 5 seconds by default.

There is an abnormal situation with a very low probability.

The central actively disconnects or abnormally disconnects the
Bluetooth connection at the same time.

At this time, the connection disconnection event will be
handled by BT RX.

At this time, sysworkq has sent a parameter update request and
will receive a reply with status = 0x02, because the handle is
invalid at this time.

We can not just cancel work, because work->flag may be
in K_WORK_RUNNING, so work->flag is set to K_WORK_CANCELING
and subsequent conn_cleanup will unable call k_work_rescheduler
successfully.

According submit_to_queue_locked will return ret = -EBUSY.

	if (flag_test(&work->flags, K_WORK_CANCELING_BIT)) {
		/* Disallowed */
		ret = -EBUSY;
As a result, the connection cannot be cleanup correctly.

Signed-off-by: Lingao Meng <menglingao@xiaomi.com>