net: xdp: report flags program was installed with on query

Some drivers enforce that flags on program replacement and
removal must match the flags passed on install.  This leaves
the possibility open to enable simultaneous loading
of XDP programs both to HW and DRV.

Allow such drivers to report the flags back to the stack.

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