selftest: fix set-attach test

After commit d6e6286a12e7 ("libbpf: disassociate section handler on explicit
bpf_program__set_type() call"), bpf_program__set_type() will force cleanup
the program's SEC() definition.

The program type should only be set if it differs from the desired one:

  if (type != BPF_PROG_TYPE_UNSPEC && bpf_program__type(prog) != type)
    bpf_program__set_type(prog, type);

selftest/set-attach/main.bpf.c

@@ -11,7 +11,7 @@ struct {
 } events SEC(".maps");
 long ringbuffer_flags = 0;
 
-SEC("fentry/FUNC")
+SEC("fentry")
 int BPF_PROG(foobar)
 {
     int *process;

selftest/set-attach/main.go

@@ -27,13 +27,17 @@ func main() {
 		os.Exit(-1)
 	}
 
-	prog.SetProgramType(bpf.BPFProgTypeTracing)
+	// eBPF program type should only be set if it differs from the desired one
+	// commit d6e6286a12e7 ("libbpf: disassociate section handler on explicit bpf_program__set_type() call")
+	// prog.SetProgramType(bpf.BPFProgTypeTracing)
 	prog.SetAttachType(bpf.BPFAttachTypeTraceFentry)
+
 	err = prog.SetAttachTarget(0, "__x64_sys_mmap")
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(-1)
 	}
+
 	err = bpfModule.BPFLoadObject()
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)