Add 868MHz envs, fix MAC id, offset timesync

src/data_model.cpp

@@ -1,9 +1,10 @@
 #include "data_model.h"
-#include <WiFi.h>
+#include <esp_mac.h>
 
 void init_device_ids(uint16_t &short_id, char *device_id, size_t device_id_len) {
   uint8_t mac[6] = {0};
-  WiFi.macAddress(mac);
+  // Read base MAC without needing WiFi to be started.
+  esp_read_mac(mac, ESP_MAC_WIFI_STA);
   short_id = (static_cast<uint16_t>(mac[4]) << 8) | mac[5];
   snprintf(device_id, device_id_len, "dd3-%04X", short_id);
 }