Expose XDP "upf_route_stat" as metrics both in prometheus and swag

[pespin]

Is your feature request related to a problem? Please describe.
XDP map upf_route_stat, which contains "struct route_stat", is not currently exported either through prometheus nor from swag web API.
This makes debugging routing problems and usual operation (eg check amount of cache hits) difficult.

Describe the solution you'd like

Have the fields of that struct available both in prometheus and swag. At least in one of them, so it can easily be debugged.