Optimize systemd dependency for containers

According to https://fedoraproject.org/wiki/Packaging:Scriptlets:
If a package is suitable for installation without systemd (in a
container image, for example) and does not require any of the
systemd mechanisms such as tmpfiles.d, then the systemd_ordering macro
MAY be used instead of the systemd_requires macro.

That is exactly the case we want to address for container images
when installing packages in it.

Resolves: rhbz#1668678
Related-Bug: #1804822
Signed-off-by: Bogdan Dobrelya <bdobreli@redhat.com>

iptables.spec

@@ -7,7 +7,7 @@
 Name: iptables
 Summary: Tools for managing Linux kernel packet filtering capabilities
 Version: 1.8.0
-Release: 3%{?dist}
+Release: 4%{?dist}
 Source: http://www.netfilter.org/projects/iptables/files/%{name}-%{version}.tar.bz2
 Source1: iptables.init
 Source2: iptables-config
@@ -77,9 +77,7 @@ stable and may change with every new version. It is therefore unsupported.
 %package services
 Summary: iptables and ip6tables services for iptables
 Requires: %{name} = %{version}-%{release}
-Requires(post): systemd
-Requires(preun): systemd
-Requires(postun): systemd
+%{?systemd_ordering}
 # obsolete old main package
 Obsoletes: %{name} < 1.4.16.1
 # obsolete ipv6 sub package
@@ -347,6 +345,9 @@ fi
 %ghost %{_sbindir}/arptables
 
 %changelog
+* Wed Jan 23 2019 Bogdan Dobrelya <bdobreli@redhat.com> - 1.8.0-4
+- Use systemd_ordering macro
+
 * Fri Jul 13 2018 Fedora Release Engineering <releng@fedoraproject.org> - 1.8.0-3
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_29_Mass_Rebuild