DOC: Explicitly state only IPv4 are supported by forwardfor/originalto options

IPv6 support was added in the 2.4. However, on previous versions, it is not
explicit that only IPv4 addresses are supported. In addition, a workaround
solution is proposed to add IPv6 addresses.

This patch is related to issue #1145. There is no upstream commit ID. It may
be backported to any stable versions.

(cherry picked from commit eac279f241289b25cc469daf04e4c309e0eb0dcb)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit f4c406b6eee0109e0c4db3f319a30530759d5bc2)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 3dd69c6..3ecfe77 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -6328,6 +6328,9 @@
   environment, as this might cause a security issue if headers reaching haproxy
   are under the control of the end-user.
 
+  Only IPv4 addresses are supported. "http-request add-header" or "http-request
+  set-header" rules may be used to work around this limitation.
+
   This option may be specified either in the frontend or in the backend. If at
   least one of them uses it, the header will be added. Note that the backend's
   setting of the header subargument takes precedence over the frontend's if
@@ -7178,6 +7181,9 @@
   network will not cause an addition of this header. Most common uses are with
   private networks or 127.0.0.1.
 
+  Only IPv4 addresses are supported. "http-request add-header" or "http-request
+  set-header" rules may be used to work around this limitation.
+
   This option may be specified either in the frontend or in the backend. If at
   least one of them uses it, the header will be added. Note that the backend's
   setting of the header subargument takes precedence over the frontend's if