stm32 targets: set preamble to 16

variants/rak3x72/target.cpp

@@ -38,7 +38,7 @@ bool radio_init() {
 
   radio.setRfSwitchTable(rfswitch_pins, rfswitch_table);
 
-  int status = radio.begin(LORA_FREQ, LORA_BW, LORA_SF, LORA_CR, RADIOLIB_SX126X_SYNC_WORD_PRIVATE, LORA_TX_POWER, 8, STM32WL_TCXO_VOLTAGE, 0); 
+  int status = radio.begin(LORA_FREQ, LORA_BW, LORA_SF, LORA_CR, RADIOLIB_SX126X_SYNC_WORD_PRIVATE, LORA_TX_POWER, 16, STM32WL_TCXO_VOLTAGE, 0); 
 
   if (status != RADIOLIB_ERR_NONE) {
     Serial.print("ERROR: radio init failed: ");