tools: bpftool: add support for loading programs for offload

Extend the bpftool prog load command to also accept "dev"
parameter, which will allow us to load programs onto devices.

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>