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-save.md

@@ -0,0 +1,17 @@
+# iptables-save
+
+> Save the `iptables` IPv4 configuration.
+> Use `ip6tables-save` to to the same for IPv6.
+> More information: <https://manned.org/iptables-save>.
+
+- Print the `iptables` configuration:
+
+`sudo iptables-save`
+
+- Print the `iptables` configuration of a specific [t]able:
+
+`sudo iptables-save --table {{table}}`
+
+- Save the `iptables` configuration to a [f]ile:
+
+`sudo iptables-save --file {{path/to/file}}`