bpftool: bpf_link_get_from_fd support for LSM programs in lskel

bpf_link_get_from_fd currently returns a NULL fd for LSM programs.
LSM programs are similar to tracing programs and can also use
skel_raw_tracepoint_open.

Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220509214905.3754984-1-kpsingh@kernel.org