tools: bpftool: fix return value when all eBPF programs have been shown

Change the program to have a more consistent return code. Specifically,
do not make bpftool return an error code simply because it reaches the
end of the list of the eBPF programs to show.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/bpf/bpftool/prog.c

@@ -275,8 +275,10 @@ static int do_show(int argc, char **argv)
 	while (true) {
 		err = bpf_prog_get_next_id(id, &id);
 		if (err) {
-			if (errno == ENOENT)
+			if (errno == ENOENT) {
+				err = 0;
 				break;
+			}
 			err("can't get next program: %s\n", strerror(errno));
 			if (errno == EINVAL)
 				err("kernel too old?\n");