Improve IPv4 and IPv6 requirements (#4224)

Author: aneta-petrova

guides/common/modules/ref_ipv6-and-ipv4-requirements.adoc

@@ -11,7 +11,7 @@ The following requirements apply to installations in an IPv4 network:
 * Ensure an IPv6 loopback is configured on the base system.
 The loopback is typically configured by default.
 Do not disable it.
-* Do not disable IPv6 in kernel by adding the `ipv6.disable=1` kernel parameter.
+Using the `ipv6.disable=1` kernel parameter or the `net.ipv6.conf.lo.disable_ipv6 = 1` sysctl option will break the installation.
 
 The following requirements apply to installations in an IPv6 network:
 
@@ -24,8 +24,10 @@ ifndef::foreman-deb,foreman-el,satellite[]
 * If you rely on content from IPv4-only networks, use an external dual-stack HTTP proxy.
 Configure {Project} to use this dual-stack (supporting both IPv4 and IPv6) HTTP proxy as the default HTTP proxy.
 endif::[]
+ifdef::katello,orcharhino,satellite[]
 * {Project} does not support configuring an HTTP proxy using a direct IPv6 address.
 Instead, configure the HTTP proxy with a FQDN that resolves to the IPv6 address.
+endif::[]
 
 If you intend to provision hosts in an IPv6 network, the following requirements also apply: