removal of systemd-units and conforming to packaging guidelines

Per announcement on fedora-devel:
https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/LLG4T53FW2BGVZLGLKNYTKPD5SQNBZ2Y/

radvd.spec

@@ -1,7 +1,7 @@
 Summary: A Router Advertisement daemon
 Name: radvd
 Version: 2.17
-Release: 6%{?dist}
+Release: 7%{?dist}
 # The code includes the advertising clause, so it's GPL-incompatible
 License: BSD with advertising
 Group: System Environment/Daemons
@@ -15,10 +15,7 @@ BuildRequires: flex
 BuildRequires: flex-static
 BuildRequires: pkgconfig
 BuildRequires: check-devel
-BuildRequires: systemd-units
-Requires(postun): systemd-units
-Requires(preun): systemd-units
-Requires(post): systemd-units
+%{?systemd_requires}
 Requires(pre): shadow-utils
 
 %description
@@ -96,6 +93,9 @@ exit 0
 %{_sbindir}/radvdump
 
 %changelog
+* Tue Jan 30 2018 Pavel Zhukov <pzhukov@redhat.com> - 2.17-7
+- removal of systemd-units and conforming to packaging guidelines
+
 * Thu Aug 03 2017 Fedora Release Engineering <releng@fedoraproject.org> - 2.17-6
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_27_Binutils_Mass_Rebuild