Log: based: Use correct local-only diff logic

cib_diff_notify() and cib_replace_notify() should use the same logic as
xml_show_patchset_header() to determine whether the diff is local-only.
The existing checks were incomplete.

We still see "local-only" diffs coming from other nodes (per the origin
field), so the terminology should be revisited at some point.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>