lib: fix on-match when added to existing route-map entry

lib: fix on-match when added to existing route-map entry

Currently, "on-match (next|goto)" only works if already present in a
route-map entry when the route-map is applied to the routes. However, if
the command is added to an existing route-map entry, the route-map is
not reapplied to the routes in order to accommodate the changes. And
service restart is needed. The problem is that setting the command
doesn't signal about the change to the listener (i.e. to a routing
daemon).

With this fix, signal to the listener about addition of "on-match
(next|goto)" to a route-map entry.

Signed-off-by: Alexander Chernavin <achernavin@netgate.com>