Downtune AsyncTCP stack size

We downtuned the stack usage of AsyncTCP, and at some point in the
history of our fork, this got folded in to the default.  Re-apply the
stack size we've been using and recover that RAM.

platformio.ini

@@ -239,6 +239,7 @@ lib_deps =
   https://github.com/Aircoookie/GifDecoder#bc3af18
 build_flags =
   -D CONFIG_ASYNC_TCP_USE_WDT=0
+  -D CONFIG_ASYNC_TCP_STACK_SIZE=8192
   -D WLED_ENABLE_GIF
 
 [esp32]