Add support for autoload libbpf APIs

[dthaler]

Describe the feature you'd like supported

libbpf.h has these APIs which are not currently supported:

LIBBPF_API bool bpf_program__autoload(const struct bpf_program *prog);
LIBBPF_API int bpf_program__set_autoload(struct bpf_program *prog, bool autoload);

Today when bpf_object__load(object) is called, all programs in the object get loaded regardless of whether they will ever be attached. If a caller only wants to use (say) one program in the object, this wastes memory and verification time.

bpf_program__set_autoload can be used to control, on a per program basis, whether bpf_object__load will or will not load the program, and bpf_program__autoload can be used to read whether it will be loaded.

Proposed solution

Implement to match equivalent functionality as standard libbpf.

Additional context

map.o for instance has 3 programs, only the last of which can actually be loaded:

C:\Users\dthal\git\ebpf\ebpf-for-windows\x64\Debug>llvm-objdump -t map.o | findstr F
0000000000000000 g     F .text  00000000000006d8 test_LRU_map
00000000000006d8 g     F .text  0000000000001890 test_PUSH_POP_map
0000000000000000 g     F sample_ext     0000000000006000 test_maps