xdp: add per mode attributes for attached programs

In preparation for support of simultaneous driver and hardware XDP
support add per-mode attributes.  The catch-all IFLA_XDP_PROG_ID
will still be reported, but user space can now also access the
program ID in a new IFLA_XDP_<mode>_PROG_ID attribute.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>