libbpf: Update API functions usage to check error

This updates usage of the following API functions within
libbpf so their newly added error return is checked:

- bpf_program__set_expected_attach_type()
- bpf_program__set_type()

Signed-off-by: Grant Seltzer <grantseltzer@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220420161226.86803-2-grantseltzer@gmail.com