changed to set the preamble on radio settings change

variants/thinknode_m2/target.cpp

@@ -44,6 +44,7 @@ void radio_set_params(float freq, float bw, uint8_t sf, uint8_t cr) {
   radio.setSpreadingFactor(sf);
   radio.setBandwidth(bw);
   radio.setCodingRate(cr);
+  radio_driver.updatePreamble(sf);
 }
 
 void radio_set_tx_power(int8_t dbm) {