Revert back to plo default arduino framework and keep custom LwIP

Settings changes for LwIP

bounjour-hap sometimes sends massive fragmented mdns packets
Change to the no-feature version of LwIP to  disable all fragmenting
and reassembly of packets.

If the TCP client suddenly goes away, LwIP will continue to send TCP
retries for about 30 minutes. This can consume up to about 4k of heap.
Use a custom lwip library that sets max tcp retries to 2, which will
quickly close the connection and free up memory in this scenerio.

lib/lwip2/README.md

@@ -0,0 +1,6 @@
+# Custom LWIP build
+This library is an exact copy of the one used in the PlatformIO Arduino framework but sets the maximum number of TCP retries to 2.
+
+This library was built from:
+https://github.com/jgstroud/Arduino/tree/maxrtx
+

platformio.ini

@@ -16,11 +16,11 @@ board_build.filesystem = littlefs
 [env:ratgdo_esp8266_hV25]
 framework = arduino
 platform = espressif8266
-platform_packages =
-    framework-arduinoespressif8266 @ https://github.com/jgstroud/Arduino.git#maxrtx
 board = d1_mini
 board_build.ldscript = eagle.flash.4m2m.ld
 build_flags =
+    -Llib/lwip2
+    -llwip2-536
     ${env.build_flags}
     '-fconcepts-ts'
     -D PIO_FRAMEWORK_ARDUINO_LWIP2_LOW_MEMORY_LOW_FLASH