pid1: when reloading configuration, forget old settings
    
    If we had a configuration setting from a configuration file, and it was
    removed, we'd still remember the old value, because there's was no mechanism to
    "reset" everything, just to assign new values.
    
    Note that the effect of this is limited. For settings that have an "ongoing" effect,
    like systemd.confirm_spawn, the new value is simply used. But some settings can only
    be set at start.
    
    In particular, CPUAffinity= will be updated if set to a new value, but if
    CPUAffinity= is fully removed, it will not be reset, simply because we don't
    know what to reset it to. We might have inherited a setting, or we might have
    set it ourselves. In principle we could remember the "original" value that was
    set when we were executed, but propagate this over reloads and reexecs, but
    that would be a lot of work for little gain. So this corner case of removal of
    CPUAffinity= is not handled fully, and a reboot is needed to execute the
    change. As a work-around, a full mask of CPUAffinity=0-8191 can be specified.
    
    (cherry picked from commit fb39af4ce42d7ef9af63009f271f404038703704)
    
    Related: #1734787
    
    patch_name: 0278-pid1-when-reloading-configuration-forget-old-setting.patch
    present_in_specfile: true
    location_in_specfile: 278
    squash_commits: true