When a fully populated LB is created, if the member is not created indicating the subnet_id to whom it belongs, the LB vip_network_id is inherit by error as member.subnet_id [1]

If the member subnet_id is indicated in the call or added after LB creation in a later step this issue is not happening.

[1] https://opendev.org/openstack/ovn-octavia-provider/blame/commit/0673f16fc68d80c364ed8907b26c061be9b8dec1/ovn_octavia_provider/driver.py#L118

How reproducible:


Steps to Reproduce:
1. Create a Fully populated LB including a member without specifying the member's subnet id
 e.g.

MY_TOKEN=$(openstack token issue | awk '/ id / {print $4}'); 
MY_OCTAVIA_PATH=$(openstack endpoint list | grep octavia | awk '/public/ {print $14}')

 curl -ks -H "x-auth-token: $MY_TOKEN" -H "Content-Type: application/json" -X POST $MY_OCTAVIA_PATH/v2.0/lbaas/loadbalancers -d'      
{                   
    "loadbalancer":{                                          
       "vip_network_id":"bf660215-faac-4c85-9abb-c9d23cb6fa16",
       "provider": "ovn",
       "name":"lb2",
       "admin_state_up":true,
       "listeners":[
          {                      
             "name": "listener2",
             "protocol":"TCP",
             "protocol_port":"80",
             "default_pool": {
                "name":"pool2",
                "protocol":"TCP",
                "lb_algorithm":"SOURCE_IP_PORT",
                "members":[{"name":"vm2","address":"192.168.200.238","protocol_port":"80"}]
             }
          }
       ]
    }
 }'


Actual results:
The member will inherit the lb.vip_network_id as member.subnet_id
OVN NB output:
_uuid               : 6bd6499d-00c1-432c-a6f7-10c499953678
external_ids        : {enabled=True, listener_2a533b18-2a26-4014-8138-057f9fb3b1ef="80:pool_2a9b0cd3-44d6-41b7-a2ef-b9dcbad02e83", lr_ref=neutron-49d8649f-e77a-4384-9047-d4b0460fdce2, ls_refs="{\"neutron-a393089b-b487-4882-9f3b-cbdc021c8f5e\": 2}", "neutron:member_status"="{\"b42c62ec-eddc-45f5-9e3b-e0f83c12f915\": \"NO_MONITOR\"}", "neutron:vip"="192.168.100.253", "neutron:vip_port_id"="285e9c8c-7216-401c-8df5-1fb3c99a159e", pool_2a9b0cd3-44d6-41b7-a2ef-b9dcbad02e83="member_b42c62ec-eddc-45f5-9e3b-e0f83c12f915_192.168.100.238:80_a393089b-b487-4882-9f3b-cbdc021c8f5e"}
health_check        : []
ip_port_mappings    : {}
name                : "7cc45497-729d-452b-8c37-d6a5e3974e8d"
options             : {}
protocol            : tcp
selection_fields    : [ip_dst, ip_src, tp_dst, tp_src]
vips                : {"192.168.100.253:80"="192.168.100.238:80"}


Expected results:
_uuid               : 6bd6499d-00c1-432c-a6f7-10c499953678
external_ids        : {enabled=True, listener_2a533b18-2a26-4014-8138-057f9fb3b1ef="80:pool_2a9b0cd3-44d6-41b7-a2ef-b9dcbad02e83", lr_ref=neutron-49d8649f-e77a-4384-9047-d4b0460fdce2, ls_refs="{\"neutron-a393089b-b487-4882-9f3b-cbdc021c8f5e\": 2}", "neutron:member_status"="{\"b42c62ec-eddc-45f5-9e3b-e0f83c12f915\": \"NO_MONITOR\"}", "neutron:vip"="192.168.100.253", "neutron:vip_port_id"="285e9c8c-7216-401c-8df5-1fb3c99a159e", pool_2a9b0cd3-44d6-41b7-a2ef-b9dcbad02e83="member_b42c62ec-eddc-45f5-9e3b-e0f83c12f915_192.168.100.238:80_0d89748e-1ed3-4fa3-a81c-f600db974e08"}
health_check        : []
ip_port_mappings    : {}
name                : "7cc45497-729d-452b-8c37-d6a5e3974e8d"
options             : {}
protocol            : tcp
selection_fields    : [ip_dst, ip_src, tp_dst, tp_src]
vips                : {"192.168.100.253:80"="192.168.100.238:80"}

This could trigger issues on operations over the member when the subnet_id is extracted from external_ids to compare to other or the future ovn-db-sync.