Bluetooth: Make sure LE create conn cancel is sent when timeout

When sending LE create conn command, we set a timer with a duration of
HCI_LE_CONN_TIMEOUT before timing out and calling
create_le_conn_complete. Additionally, when receiving the command
complete, we also set a timer with the same duration to call
le_conn_timeout.

Usually the latter will be triggered first, which then sends a LE
create conn cancel command. However, due to the nature of racing, it
is possible for the former to be called first, thereby calling the
chain hci_conn_failed -> hci_conn_del -> cancel_delayed_work, thereby
preventing LE create conn cancel to be sent. In this situation, the
controller will be stuck in trying the LE connection.

This patch flushes le_conn_timeout on create_le_conn_complete to make
sure we always send LE create connection cancel, if necessary.

Signed-off-by: Archie Pusaka <apusaka@chromium.org>
Reviewed-by: Ying Hsu <yinghsu@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>