feat: add automatic network failover

variants/thinknode_m7/platformio.ini

@@ -190,7 +190,7 @@ build_src_filter = ${ThinkNode_M7.build_src_filter}
   +<../examples/kiss_modem/>
 
 ; Wi-Fi remains the default observer transport. Ethernet twins below select the
-; onboard CH390 through NETWORK_USE_ETHERNET without enabling the legacy CLI
+; onboard CH390 through the Ethernet-preferred network manager without enabling the legacy CLI
 ; transport. The board has PSRAM, so MAX_NEIGHBOURS enables
 ; WITH_MQTT_NEIGHBORS (see MQTTBridge.h).
 [env:ThinkNode_M7_repeater_observer_mqtt]
@@ -242,7 +242,7 @@ extends = env:ThinkNode_M7_repeater_observer_mqtt
 build_flags =
   ${env:ThinkNode_M7_repeater_observer_mqtt.build_flags}
   ${ThinkNode_M7_ch390.build_flags}
-  -D NETWORK_USE_ETHERNET=1
+  -D NETWORK_PREFER_ETHERNET=1
 build_src_filter = ${env:ThinkNode_M7_repeater_observer_mqtt.build_src_filter}
 lib_deps =
   ${env:ThinkNode_M7_repeater_observer_mqtt.lib_deps}
@@ -298,7 +298,7 @@ extends = env:ThinkNode_M7_room_server_observer_mqtt
 build_flags =
   ${env:ThinkNode_M7_room_server_observer_mqtt.build_flags}
   ${ThinkNode_M7_ch390.build_flags}
-  -D NETWORK_USE_ETHERNET=1
+  -D NETWORK_PREFER_ETHERNET=1
 build_src_filter = ${env:ThinkNode_M7_room_server_observer_mqtt.build_src_filter}
 lib_deps =
   ${env:ThinkNode_M7_room_server_observer_mqtt.lib_deps}