Step 3.3a: PTP servo, clock locks to the GM

- ptp_hw: ptp_hw_adj_freq() (ETH_MAC_ESP_CMD_ADJ_PTP_TIME, absolute ppb
  vs nominal, clamped +-500 ppm, retried while the addend update is
  busy) and ptp_hw_step() (read + write time).
- ptp_clock: first Sync after a GM is selected seeds the integral with
  the measured rate and steps the clock; then linuxptp-style PI (kp/ki
  from the Sync interval: 0.7/0.3 at 1 s). Re-step above 1 ms. Locked
  after 8 Syncs with |offset| < 1 us, unlocked after 3 above; GM change
  or loss unlocks and keeps the frequency (holdover).
- Verified vs ptp4l: stepped to GM time, locked after ~19 s; locked
  offset within +-510 ns (mostly < 300 ns), correction +39.9 ppm
  (crystal -39.8 ppm), path delay ~10.2 us.

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

components/aes67_ptp/ptp_hw.c

@@ -77,6 +77,38 @@ esp_err_t ptp_hw_get_time(eth_mac_time_t *t)
     return esp_eth_ioctl(s_eth, ETH_MAC_ESP_CMD_G_PTP_TIME, t);
 }
 
+esp_err_t ptp_hw_adj_freq(double ppb)
+{
+    if (ppb > 500000) {
+        ppb = 500000;       // +-500 ppm is far outside any sane crystal
+    } else if (ppb < -500000) {
+        ppb = -500000;
+    }
+    int32_t v = (int32_t)(ppb >= 0 ? ppb + 0.5 : ppb - 0.5);
+    esp_err_t err = ESP_ERR_INVALID_STATE;
+    // The previous addend update may still be in progress: retry briefly.
+    for (int i = 0; i < 10 && err == ESP_ERR_INVALID_STATE; i++) {
+        err = esp_eth_ioctl(s_eth, ETH_MAC_ESP_CMD_ADJ_PTP_TIME, &v);
+    }
+    return err;
+}
+
+esp_err_t ptp_hw_step(int64_t offset_ns)
+{
+    eth_mac_time_t t;
+    esp_err_t err = ptp_hw_get_time(&t);
+    if (err != ESP_OK) {
+        return err;
+    }
+    int64_t ns = (int64_t)t.seconds * 1000000000LL + t.nanoseconds - offset_ns;
+    if (ns < 0) {
+        return ESP_ERR_INVALID_ARG;
+    }
+    t.seconds = ns / 1000000000LL;
+    t.nanoseconds = ns % 1000000000LL;
+    return esp_eth_ioctl(s_eth, ETH_MAC_ESP_CMD_S_PTP_TIME, &t);
+}
+
 static uint16_t ip_checksum(const uint8_t *h, size_t len)
 {
     uint32_t sum = 0;