iptables: update page; ip6tables, ip{6,}tables-{restore,save}: add page (#10715)

* iptables: update page

* iptables-{restore,save}: add page

* ip6tables, ip6tables-{restore,save}: add alias page

* iptables-save: remove trailing whitespace

pages/linux/iptables-restore.md

@@ -0,0 +1,9 @@
+# iptables-restore
+
+> Restore the `iptables` IPv4 configuration.
+> Use `ip6tables-restore` to do the same for IPv6.
+> More information: <https://manned.org/iptables-restore>.
+
+- Restore the `iptables` configuration from a file:
+
+`sudo iptables-restore {{path/to/file}}`