doc: fix "ipv6 address" interface command syntax (#608)
(cherry picked from commit e6844aa5d23cf56dd1f31afc96e8145ab188953f)
diff --git a/doc/main.texi b/doc/main.texi
index 9966b35..a575913 100644
--- a/doc/main.texi
+++ b/doc/main.texi
@@ -49,9 +49,9 @@
 @end deffn
 
 @deffn {Interface Command} {ip address @var{address/prefix}} {}
-@deffnx {Interface Command} {ip6 address @var{address/prefix}} {}
+@deffnx {Interface Command} {ipv6 address @var{address/prefix}} {}
 @deffnx {Interface Command} {no ip address @var{address/prefix}} {}
-@deffnx {Interface Command} {no ip6 address @var{address/prefix}} {}
+@deffnx {Interface Command} {no ipv6 address @var{address/prefix}} {}
 Set the IPv4 or IPv6 address/prefix for the interface.
 @end deffn