Disable IGMP snooping to avoid issues with DHCPv6

In OSP 17.1 we cannot combine Ironic provisioning and
IGMP snooping. See the Jira ticket for details.

This change sets `NeutronEnableIgmpSnooping: false`

Jira: OSPRH-25988
Signed-off-by: Harald Jensås <hjensas@redhat.com>

Author: hjensas

scenarios/uni04delta-ipv6/config_download.yaml

@@ -66,7 +66,8 @@ parameter_defaults:
   ComputeHostnameFormat: '%stackname%-compute-%index%'
   EnableVLANTransparency: true
   NeutronServicePlugins: 'qos,ovn-router,trunk,segments,log'
-  NeutronEnableIgmpSnooping: true
+  # OSPRH-25988: Disable IGMP snooping to avoid issues with DHCPv6
+  NeutronEnableIgmpSnooping: false
   OVNEmitNeedToFrag: false
   NeutronNetworkVLANRanges: 'datacentre:1000:2000'
   NeutronTypeDrivers: 'geneve,vlan,flat,local'