Export bpf_program__attach_kprobe_opts as a public API.

Rename bpf_program_attach_kprobe_opts to bpf_kprobe_opts and turn it into OPTS
struct.
Suggested-by: NAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Signed-off-by: NAndrii Nakryiko <andrii@kernel.org>
Reviewed-by: NAlan Maguire <alan.maguire@oracle.com>
Tested-by: NAlan Maguire <alan.maguire@oracle.com>
Link: https://lore.kernel.org/bpf/20210721215810.889975-4-jolsa@kernel.org