Description of problem:
extra-dhcp-option classless-static-route is not working properly. It sets the value in the SBDB without {} and overrides default routes.

Version-Release number of selected component (if applicable):
Red Hat Openstack Platform 16 (RHOSP16)
Red Hat Openstack Platform 17 (RHOSP17)

Steps to Reproduce:
1. after port creation:
~~~
ovn-sbctl --db=$SBDB find logical_flow external_ids:stage-name=ls_in_dhcp_options | grep -B 2 -A 6 192.168.210.114
_uuid               : 57c306d2-5e5b-460b-b314-9e581bb44e12
actions             : "reg0[3] = put_dhcp_opts(offerip = 192.168.210.114, classless_static_route = {169.254.169.254/32,192.168.210.100, 0.0.0.0/0,192.168.210.1}, dns_server = {172.16.0.1, 10.0.0.1}, lease_time = 43200, mtu = 1442, netmask = 255.255.255.0, router = 192.168.210.1, server_id = 192.168.210.1); next;"
--
_uuid               : cbe4a7b9-6536-4a28-833c-b941eecd7886
actions             : "reg0[3] = put_dhcp_opts(offerip = 192.168.210.114, classless_static_route = {169.254.169.254/32,192.168.210.100, 0.0.0.0/0,192.168.210.1}, dns_server = {172.16.0.1, 10.0.0.1}, lease_time = 43200, mtu = 1442, netmask = 255.255.255.0, router = 192.168.210.1, server_id = 192.168.210.1); next;"
~~~
2. then if we set a set static route:
~~~
openstack port set --extra-dhcp-option name=classless-static-route,value=128.128.128.128/32,22.2.0.2,ip-version=4 a02943c7-6761-43ed-bcfd-2ac01afd2cb8
~~~
3. We will lose the default static route and it creates a syntax error because remove the {}
~~~
[root@compute-1 /]# ovn-sbctl --db=$SBDB find logical_flow external_ids:stage-name=ls_in_dhcp_options | grep -B 2 -A 6 192.168.210.114

_uuid               : 8ead0f38-60fa-4d4e-88d1-63c39a03563f
actions             : "reg0[3] = put_dhcp_opts(offerip = 192.168.210.114, classless_static_route = 128.128.128.128/32,22.2.0.2, dns_server = {172.16.0.1, 10.0.0.1}, lease_time = 43200, mtu = 1442, netmask = 255.255.255.0, router = 192.168.210.1, server_id = 192.168.210.1); next;"
--
_uuid               : 36084950-18f7-4c41-9142-e34abdae4094
actions             : "reg0[3] = put_dhcp_opts(offerip = 192.168.210.114, classless_static_route = 128.128.128.128/32,22.2.0.2, dns_server = {172.16.0.1, 10.0.0.1}, lease_time = 43200, mtu = 1442, netmask = 255.255.255.0, router = 192.168.210.1, server_id = 192.168.210.1); next;"
~~~
4. we can see the syntax error in the logs:
~~~
2024-05-27T08:53:12.951Z|328987|lflow|WARN|error parsing actions "reg0[3] = put_dhcp_opts(offerip = 192.168.210.114, classless_static_route = 128.128.128.128/32,22.2.0.2, dns_server = {192.168.210.212, 192.168.210.213}, lease_time = 43200, mtu = 1500, netmask = 255.255.255.0, router = 192.168.210.1, server_id = 192.168.210.1, tftp_server_address = 10.0.0.1); next;": Syntax error at `22.2.0.2'.
~~~

Actual results:
extra-dhcp-option classless-static-route is not working

Expected results:
extra-dhcp-option classless-static-route should add the new static route at the end.

Additiona info:
as a Workaround I pass the static route with the default one in the {}, something like:
~~~
openstack port set --extra-dhcp-option name=classless-static-route,value="{169.254.169.254/32,192.168.210.100,0.0.0.0/0,192.168.210.1,128.128.128.128/32,22.2.0.2},ip-version=4" a02943c7-6761-43ed-bcfd-2ac01afd2cb8
~~~