cidata: mark slirp NIC as optional to fix ubuntu-26.04 first-boot delay

On ubuntu-26.04, systemd-networkd-wait-online is configured by netplan to
wait for eth0 before it exists. On first boot the NIC is still enp0s1 —
the udev rename hasn't happened yet — causing a 120s timeout.

Marking the slirp NIC as optional (netplan optional: true ->
RequiredForOnline=no in systemd-networkd) tells wait-online to not block
on eth0, so boot completes immediately. The interface is still renamed to
eth0 after boot, preserving existing behaviour for all other tools.

Fixes: #4792

Signed-off-by: Ramadhan Gerry Akbar <ramadhan.gerry@gmail.com>

Author: itsme-ranger

hack/test-templates.sh

@@ -229,7 +229,7 @@ if [[ -n ${CHECKS["proxy-settings"]} ]]; then
 	got=$(limactl shell "$NAME" env | grep FTP_PROXY)
 	# Expected: FTP_PROXY is set in addition to ftp_proxy, localhost is replaced
 	# by the gateway address, and the value is set immediately without a restart
-	gatewayIp=$(limactl shell "$NAME" ip route show 0.0.0.0/0 dev eth0 | cut -d\  -f3)
+	gatewayIp=$(limactl shell "$NAME" ip route show 0.0.0.0/0 | awk '{print $3; exit}')
 	expected="FTP_PROXY=http://${gatewayIp}:2121"
 	INFO "FTP_PROXY: expected=${expected} got=${got}"
 	if [ "$got" != "$expected" ]; then

pkg/cidata/cidata.TEMPLATE.d/network-config

@@ -5,6 +5,9 @@ ethernets:
     match:
       macaddress: '{{$nw.MACAddress}}'
     dhcp4: true
+    {{- if eq $nw.Interface $.SlirpNICName }}
+    optional: true
+    {{- end }}
     set-name: {{$nw.Interface}}
     dhcp4-overrides:
       route-metric: {{$nw.Metric}}