Backport multipath route support from nm-1-36 to nm-1-34 to fix https://bugzilla.redhat.com/show_bug.cgi?id=2091885
Conflicts:
- nm-1-34 doesn't have a2030c01 ("platform: add support for blackhole,unreachable,prohibit route type") and so
new_from_nl_route()needed manual resolution in last commit; - IS_IPv4 rename also needed manual adjustments due to different identation.