[SX128x] Fixed known binary receive length

src/modules/SX128x/SX128x.cpp

@@ -573,9 +573,10 @@ int16_t SX128x::readData(uint8_t* data, size_t len) {
   }
 
   // get packet length
-  size_t length = len;
+  size_t length = getPacketLength();
-  if(len == RADIOLIB_SX128X_MAX_PACKET_LENGTH) {
+  if((len != 0) && (len < length)) {
-    length = getPacketLength();
+    // user requested less data than we got, only return what was requested
+    length = len;
   }
 
   // read packet data

src/modules/SX128x/SX128x.h

@@ -567,7 +567,8 @@ class SX128x: public PhysicalLayer {
 
       \param data Pointer to array to save the received binary data.
 
-      \param len Number of bytes that will be received. Must be known in advance for binary transmissions.
+      \param len Number of bytes that will be read. When set to 0, the packet length will be retreived automatically.
+      When more bytes than received are requested, only the number of bytes requested will be returned.
 
       \returns \ref status_codes
     */