fix(devcontainer): fix devcontainer under ubuntu 26.04 - iptables changes

nat': Table does not exist (do you need to insmod?)\nPerhaps iptables or your kernel needs to be upgraded.\n (exit status 3)

Author: Stephen Mott

src/docker-in-docker/install.sh

@@ -310,10 +310,16 @@ if [ "${ADJUSTED_ID}" = "debian" ] && command -v update-ca-certificates > /dev/n
     update-ca-certificates
 fi
 
-# Swap to legacy iptables for compatibility (Debian only)
 if [ "${ADJUSTED_ID}" = "debian" ] && type iptables-legacy > /dev/null 2>&1; then
-    update-alternatives --set iptables /usr/sbin/iptables-legacy
-    update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy
+    # Check if host kernel supports ip_tables/iptable_nat
+    if iptables-legacy -t nat -L > /dev/null 2>&1; then
+        update-alternatives --set iptables /usr/sbin/iptables-legacy
+        update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy
+    else
+        # first appeared in Ubuntu ≥ 26.04
+        update-alternatives --set iptables  /usr/sbin/iptables-nft
+        update-alternatives --set ip6tables /usr/sbin/ip6tables-nft
+    fi
 fi
 
 # Set up the necessary repositories