added the preamble update into get est airtime as a prevention for false airtime calcs. Left update in the startsendraw as a safety, but should not be used under normal circumstances

src/helpers/radiolib/RadioLibWrappers.cpp

@@ -139,6 +139,11 @@ int RadioLibWrapper::recvRaw(uint8_t* bytes, int sz) {
 }
 
 uint32_t RadioLibWrapper::getEstAirtimeFor(int len_bytes) {
+  uint8_t sf = getSpreadingFactor();
+  if (sf != _preamble_sf) {
+    _preamble_sf = sf;
+    _radio->setPreambleLength(preambleLengthForSF(sf)); // sync preamble before airtime estimate
+  }
   return _radio->getTimeOnAir(len_bytes) / 1000;
 }