bpf: keep parsed program mode in struct bpf_cfg_in

bpf: keep parsed program mode in struct bpf_cfg_in

bpf_parse() will parse command line arguments to find out the
program mode.  This mode will later be needed at loading time.
Instead of keeping it locally add it to struct bpf_cfg_in,
this will allow splitting parsing and loading stages.

enum bpf_mode has to be moved to the header file, because C
doesn't allow forward declaration of enums.

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