Only compile WiFi related filters when WiFi is available

[mathieucarbou]

@mathieucarbou @qniens

The P4 env needs a change

[env:esp32-p4]
platform = espressif32
framework = arduino
board = esp32-p4
build_flags = -DLED_BUILTIN=2
monitor_speed = 115200
lib_deps =                https://github.com/ESP32Async/AsyncTCP.git
                          https://github.com/ESP32Async/ESPAsyncWebServer.git
custom_sdkconfig =        CONFIG_ESP_HOST_WIFI_ENABLED=y
                          CONFIG_ESP_MAIN_TASK_STACK_SIZE=7168

The key is to enable Host wifi for the P4. Now ESPAsyncWebServer throws an error

.pio/libdeps/esp32-p4/ESPAsyncWebServer/src/WebServer.cpp:11:10: error: 'WiFi' was not declared in this scope
   11 |   return WiFi.localIP() == request->client()->localIP();
      |          ^~~~
.pio/libdeps/esp32-p4/ESPAsyncWebServer/src/WebServer.cpp: In function 'bool ON_AP_FILTER(AsyncWebServerRequest*)':
.pio/libdeps/esp32-p4/ESPAsyncWebServer/src/WebServer.cpp:19:10: error: 'WiFi' was not declared in this scope
   19 |   return WiFi.localIP() != request->client()->localIP();
      |          ^~~~

This line https://github.com/ESP32Async/ESPAsyncWebServer/blob/c25ff116ab0ee917b43ade6156e3bac9e7e80611/src/WebServer.cpp#L10 (probably other too) needs a specifi check for the P4 which Network is used Wifi / ETH

Originally posted by @Jason2866 in #67 (comment)