It is no longer necessary to detect the server version in the spec file, thus the solution is cleaner. OBS-URL: https://build.opensuse.org/package/show/Virtualization/virtualbox?expand=0&rev=299
The spec file now interrogates the rpm for the server and conditionally applies the patch, thus both versions build OK. OBS-URL: https://build.opensuse.org/package/show/Virtualization/virtualbox?expand=0&rev=297