Segment of ha network is deleted when a ha router is removed

[sunzuohua]

The repro steps is as follows:
1.Create at least two ha router.
2.Delete one ha router.

Then the ha network is not deleted, but the segment of this ha network is deleted.
[root@cdpm01 ~]# neutron net-show 5edf9be2-2a07-4350-98dd-9d3c12a9b9dd
neutron CLI is deprecated and will be removed in the future. Use openstack CLI instead.
+---------------------------+----------------------------------------------------+
| Field | Value |
+---------------------------+----------------------------------------------------+
| admin_state_up | True |
| availability_zone_hints | |
| availability_zones | nova |
| created_at | 2017-11-17T01:40:44Z |
| description | |
| id | 5edf9be2-2a07-4350-98dd-9d3c12a9b9dd |
| ipv4_address_scope | |
| ipv6_address_scope | |
| mtu | 1450 |
| name | HA network tenant a2794be2207a45b5be5b2423bfa08c2c |
| port_security_enabled | True |
| project_id | |
| provider:network_type | |
| provider:physical_network | |
| provider:segmentation_id | |
| qos_policy_id | |
| revision_number | 5 |
| router:external | False |
| shared | False |
| status | ACTIVE |
| subnets | a356ecf7-c4a0-4596-b742-d1521a2aa38f |
| tags | |
| tenant_id | |
| updated_at | 2017-11-17T09:26:25Z |
+---------------------------+----------------------------------------------------+

The reason:
1.When a ha router is deleted, neutron attempted to delete the ha network.
2.When deleting a network, the event:events.BEFORE_DELETE for resources.NETWORK is send[[1]] and _delete_segments_for_network is invoked to delete the segment[2].
3.After sending the event:events.BEFORE_DELETE for resources.NETWORK, the ha network is checked to be in use[3], so it is not deleted

Mybe we should check if the network is in use before sending the event:events.BEFORE_DELETE for resources.NETWORK?
Or Check if the router being deleted is the last router belong to the tenant.

[1]https://github.com/openstack/neutron/blob/master/neutron/db/db_base_plugin_v2.py#L433
[2]https://github.com/openstack/neutron/blob/master/neutron/services/segments/db.py#L315
[3]https://github.com/openstack/neutron/blob/master/neutron/db/db_base_plugin_v2.py#L435