bgpd: fix default-originate route-map processing

bgpd: fix default-originate route-map processing

When processing a route-map for default-originate, we actually want to
match by attributes in routes from the RIB, but set attributes in the
newly originated route. Currently, it's not the case. Instead, we
construct a dummy path combining attributes from both routes, and we end
up with multiple problems:
- match by as-path doesn't work
- communities from the matched RIB route are copied to the newly
  originated route
- we corrupt the RIB routes

To fix the issue, we should use the new route-map API that allows using
separate match/set objects.

Fixes #9584.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>