fix: handle empty network_group and ipv6_interface_type for WAN networks

WAN networks return empty values for these fields from the API, causing
perpetual drift against schema defaults. Now explicitly set defaults
when API returns empty for WAN networks.

internal/provider/network/resource_network.go

@@ -724,7 +724,12 @@ func resourceNetworkSetResourceData(resp *unifi.Network, d *schema.ResourceData,
 	d.Set("purpose", resp.Purpose)
 	d.Set("vlan_id", vlan)
 	d.Set("subnet", utils.CidrZeroBased(resp.IPSubnet))
-	d.Set("network_group", resp.NetworkGroup)
+
+	networkGroup := resp.NetworkGroup
+	if resp.Purpose == "wan" && networkGroup == "" {
+		networkGroup = "LAN"
+	}
+	d.Set("network_group", networkGroup)
 
 	d.Set("dhcp_dns", dhcpDNS)
 	d.Set("dhcp_enabled", resp.DHCPDEnabled)
@@ -746,7 +751,12 @@ func resourceNetworkSetResourceData(resp *unifi.Network, d *schema.ResourceData,
 	d.Set("igmp_snooping", resp.IGMPSnooping)
 	d.Set("internet_access_enabled", resp.InternetAccessEnabled)
 	d.Set("network_isolation_enabled", resp.NetworkIsolationEnabled)
-	d.Set("ipv6_interface_type", resp.IPV6InterfaceType)
+
+	ipv6InterfaceType := resp.IPV6InterfaceType
+	if resp.Purpose == "wan" && ipv6InterfaceType == "" {
+		ipv6InterfaceType = "none"
+	}
+	d.Set("ipv6_interface_type", ipv6InterfaceType)
 	d.Set("ipv6_pd_interface", resp.IPV6PDInterface)
 	d.Set("ipv6_pd_prefixid", resp.IPV6PDPrefixid)
 	d.Set("ipv6_pd_start", resp.IPV6PDStart)