convert GPLv2+ license to SPDX

This is part of https://fedoraproject.org/wiki/Changes/SPDX_Licenses_Phase_4

strongswan.spec

@@ -16,9 +16,10 @@
 
 Name:           strongswan
 Version:        5.9.14
-Release:        3%{?dist}
+Release:        4%{?dist}
 Summary:        An OpenSource IPsec-based VPN and TNC solution
-License:        GPLv2+
+# Automatically converted from old format: GPLv2+ - review is highly recommended.
+License:        GPL-2.0-or-later
 URL:            https://www.strongswan.org/
 VCS:            git:%{forgeurl0}
 Source0:        https://download.strongswan.org/strongswan-%{version}%{?prerelease}.tar.bz2
@@ -416,6 +417,9 @@ install -D -m 0644 %{SOURCE3} %{buildroot}/%{_tmpfilesdir}/strongswan-starter.co
 %endif
 
 %changelog
+* Fri Jul 26 2024 Miroslav Suchý <msuchy@redhat.com> - 5.9.14-4
+- convert license to SPDX
+
 * Sat Jul 20 2024 Fedora Release Engineering <releng@fedoraproject.org> - 5.9.14-3
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_41_Mass_Rebuild