[ethernet][network][wifi] Arbitrate the default route from the network priority list (#17797)

tests/components/network/test-priority.esp32-ard.yaml

@@ -0,0 +1,23 @@
+# Arduino dual-stack test: default-route arbitration must also compile under
+# the Arduino framework, which builds the same esp_netif/ESP-IDF from source.
+# Ethernet is listed first so this build exercises the ethernet-first side of
+# the arbitration pivot in NetworkComponent::loop() (the IDF variant of this
+# test covers the wifi-first side).
+wifi:
+  ssid: MySSID
+  password: password1
+
+ethernet:
+  type: W5500
+  clk_pin: GPIO19
+  mosi_pin: GPIO21
+  miso_pin: GPIO23
+  cs_pin: GPIO18
+  interrupt_pin: GPIO36
+  reset_pin: GPIO22
+  clock_speed: 10Mhz
+
+network:
+  priority:
+    - ethernet
+    - wifi