doc: document the -4 and -6 options

Signed-off-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/iptables/ip6tables.8.in b/iptables/ip6tables.8.in
index 8f04b31..58b7bfc 100644
--- a/iptables/ip6tables.8.in
+++ b/iptables/ip6tables.8.in
@@ -240,6 +240,15 @@
 The following parameters make up a rule specification (as used in the
 add, delete, insert, replace and append commands).
 .TP
+\fB\-4\fP, \fB\-\-ipv4\fP
+If a rule using the \fB\-4\fP option is inserted with (and only with)
+ip6tables-restore, it will be silently ignored. Any other uses will throw an
+error. This option allows to put both IPv4 and IPv6 rules in a single rule file
+for use with both iptables-restore and ip6tables-restore.
+.TP
+\fB\-6\fP, \fB\-\-ipv6\fP
+This option has no effect in ip6tables and ip6tables-restore.
+.TP
 [\fB!\fP] \fB\-p\fP, \fB\-\-protocol\fP \fIprotocol\fP
 The protocol of the rule or of the packet to check.
 The specified protocol can be one of \fBtcp\fP, \fBudp\fP, \fBudplite\fP,
diff --git a/iptables/iptables.8.in b/iptables/iptables.8.in
index 8d65764..013ac77 100644
--- a/iptables/iptables.8.in
+++ b/iptables/iptables.8.in
@@ -243,6 +243,15 @@
 The following parameters make up a rule specification (as used in the
 add, delete, insert, replace and append commands).
 .TP
+\fB\-4\fP, \fB\-\-ipv4\fP
+This option has no effect in iptables and iptables-restore.
+.TP
+\fB\-6\fP, \fB\-\-ipv6\fP
+If a rule using the \fB\-6\fP option is inserted with (and only with)
+iptables-restore, it will be silently ignored. Any other uses will throw an
+error. This option allows to put both IPv4 and IPv6 rules in a single rule file
+for use with both iptables-restore and ip6tables-restore.
+.TP
 [\fB!\fP] \fB\-p\fP, \fB\-\-protocol\fP \fIprotocol\fP
 The protocol of the rule or of the packet to check.
 The specified protocol can be one of \fBtcp\fP, \fBudp\fP, \fBudplite\fP,