Fix POE boot failure on RAK4631 Ethernet builds

Drive WB_IO2 (slot power switch) HIGH via early constructor before the
Arduino framework initializes. Without this, the board brownouts on
POE-only power because the slot MOSFET isn't enabled early enough for
the RAK13800 POE module to deliver power to the baseboard.

Also remove the W5100S hardware reset pulse from Ethernet init — the
chip comes out of power-on reset cleanly, and toggling reset kills
the PHY link which breaks POE power delivery.

variants/rak4631/RAK4631Board.cpp

@@ -1,8 +1,21 @@
 #include <Arduino.h>
 #include <Wire.h>
+#include "nrf_gpio.h"
 
 #include "RAK4631Board.h"
 
+#ifdef ETHERNET_ENABLED
+// Drive WB_IO2 HIGH as early as possible using direct register access.
+// WB_IO2 (P1.02, Arduino pin 34) controls the WisBlock slot power switch.
+// With POE through RAK13800, this must be enabled before the framework
+// initializes or the board will brownout from insufficient power delivery.
+// Priority 102 runs just after SystemInit.
+static void __attribute__((constructor(102))) rak4631_early_poe_power() {
+  nrf_gpio_cfg_output(NRF_GPIO_PIN_MAP(1, 2));  // WB_IO2 = P1.02
+  nrf_gpio_pin_set(NRF_GPIO_PIN_MAP(1, 2));
+}
+#endif
+
 #ifdef NRF52_POWER_MANAGEMENT
 // Static configuration for power management
 // Values set in variant.h defines