samples: bpf: improve xdp1 example

static void poll_stats(int map_fd, int interval)

{

	unsigned int nr_cpus = bpf_num_possible_cpus();

	const unsigned int nr_keys = 256;

	__u64 values[nr_cpus], prev[nr_keys][nr_cpus];

	__u32 key;

	__u64 values[nr_cpus], prev[UINT8_MAX] = { 0 };

	int i;

	memset(prev, 0, sizeof(prev));

	while (1) {

		__u32 key = UINT32_MAX;

		sleep(interval);

		for (key = 0; key < nr_keys; key++) {

		while (bpf_map_get_next_key(map_fd, &key, &key) != -1) {

			__u64 sum = 0;

			assert(bpf_map_lookup_elem(map_fd, &key, values) == 0);

			for (i = 0; i < nr_cpus; i++)

				sum += (values[i] - prev[key][i]);

			if (sum)

				sum += values[i];

			if (sum > prev[key])

				printf("proto %u: %10llu pkt/s\n",

				       key, sum / interval);

			memcpy(prev[key], values, sizeof(values));

				       key, (sum - prev[key]) / interval);

			prev[key] = sum;

		}

	}

}