Add an ESP32_CPU_FREQ build flag to lower freq

platformio.ini

@@ -126,6 +126,7 @@ build_flags =
   -D SX126X_DIO3_TCXO_VOLTAGE=1.8
   -D SX126X_CURRENT_LIMIT=130.0f  ; for best TX power!
   -D SX126X_RX_BOOSTED_GAIN=true
+  -D ESP32_CPU_FREQ=240
 build_src_filter = ${esp32_base.build_src_filter}
 lib_deps =
   ${esp32_base.lib_deps}