selftests/bpf: xdp_hw_metadata reduce sleep interval

In current ping-pong design, xdp_hw_metadata will wait until the packet
transmission completely done, then only start to receive the next packet.

The current sleep interval is 10ms, which is unnecessary large. Typically,
a NIC does not need such a long time to transmit a packet. Furthermore,
during this 10ms sleep time, the app is unable to receive incoming packets.

Therefore, this commit reduce sleep interval to 10us, so that
xdp_hw_metadata is able to support periodic packets with shorter interval.
10us * 500 = 5ms should be enough for packet transmission and status
retrieval.
Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20240303083225.1184165-2-yoong.siang.song@intel.com

tools/testing/selftests/bpf/xdp_hw_metadata.c

@@ -480,7 +480,7 @@ static int verify_metadata(struct xsk *rx_xsk, int rxq, int server_fd, clockid_t
 					for (int j = 0; j < 500; j++) {
 						if (complete_tx(xsk, clock_id))
 							break;
-						usleep(10*1000);
+						usleep(10);
 					}
 				}
 			}