manifests: add iptables-nft.yaml for f36+

Add a new conditional include which migrates streams on Fedora 36 and
higher to iptables-nft. This is magnitudes simpler than the current
alternative rollout procedure detailed in:

coreos/fedora-coreos-tracker#676

manifests/fedora-coreos-base.yaml

@@ -17,6 +17,11 @@ ostree-layers:
   - overlay/14NetworkManager-plugins
   - overlay/20platform-chrony
 
+conditional-include:
+  # https://github.com/coreos/fedora-coreos-tracker/issues/676
+  - if: releasever >= 36
+    include: iptables-nft.yaml
+
 initramfs-args:
   - --no-hostonly
   # We don't support root on NFS, so we don't need it in the initramfs. It also

manifests/iptables-nft.yaml

@@ -0,0 +1,17 @@
+# Scripts for opting into staying on iptables-legacy after migration. Remove
+# after the next barrier release.
+ostree-layers:
+  - overlay/35coreos-iptables
+
+# Default to iptables-nft. Otherwise, legacy wins. We can drop this once/if we
+# remove iptables-legacy.
+postprocess:
+- |
+  #!/usr/bin/env bash
+  set -xeuo pipefail
+  ln -sf /usr/sbin/ip6tables-nft         /etc/alternatives/ip6tables
+  ln -sf /usr/sbin/ip6tables-nft-restore /etc/alternatives/ip6tables-restore
+  ln -sf /usr/sbin/ip6tables-nft-save    /etc/alternatives/ip6tables-save
+  ln -sf /usr/sbin/iptables-nft          /etc/alternatives/iptables
+  ln -sf /usr/sbin/iptables-nft-restore  /etc/alternatives/iptables-restore
+  ln -sf /usr/sbin/iptables-nft-save     /etc/alternatives/iptables-save