Step 3.1: EMAC hardware timestamps for PTP over UDP/IPv4

- aes67_ptp/ptp_hw.c: start the EMAC IEEE 1588 clock (IDF
  ETH_MAC_ESP_CMD_PTP_ENABLE) and additionally enable snapshots for
  PTP over UDP/IPv4 (IDF only enables PTP over Ethernet/L2). An RX hook
  on the driver's info input path records {type, seq, sourcePortId, HW
  timestamp} of port-319 PTPv2 event messages, then hands every frame to
  lwIP unchanged.
- aes67_ptp.c: temporary 3.1 logger joins 224.0.1.129:319/320 and pairs
  Sync HW RX timestamps with Follow_Up origin timestamps.
- Checked against linuxptp ptp4l (-4 -E -H, Intel igb) as GM: every Sync
  has a HW timestamp; HW Sync intervals track the GM intervals with a
  constant -39.8 us/s (+-0.3 us), i.e. local clock -39.8 ppm vs GM.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

components/aes67_ptp/ptp_hw.h

@@ -0,0 +1,22 @@
+// EMAC IEEE 1588 clock and hardware timestamps for PTP over UDP/IPv4.
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "esp_eth_driver.h"
+#include "esp_eth_mac.h"
+#include "esp_netif.h"
+
+#define PTP_MSG_SYNC        0x0
+#define PTP_MSG_DELAY_REQ   0x1
+#define PTP_MSG_FOLLOW_UP   0x8
+#define PTP_MSG_DELAY_RESP  0x9
+#define PTP_MSG_ANNOUNCE    0xB
+
+// Start the EMAC PTP clock, enable IPv4/UDP timestamping and hook the RX path.
+esp_err_t ptp_hw_init(esp_eth_handle_t eth, esp_netif_t *netif);
+// Hardware RX timestamp of an event message (UDP port 319), looked up by type,
+// sequence ID and sourcePortIdentity (10 bytes). Each record is returned once.
+bool ptp_hw_rx_ts(uint8_t msg_type, uint16_t seq, const uint8_t *src_port_id, eth_mac_time_t *ts);
+esp_err_t ptp_hw_get_time(eth_mac_time_t *t);