Correct TransportRecv_t documentation

Corrections highlight the non-blocking
expectations of the TransportRecv method.

Inspired by - FreeRTOS#261

source/interface/transport_interface.h

@@ -195,14 +195,10 @@ typedef struct NetworkContext NetworkContext_t;
  * @transportcallback
  * @brief Transport interface for receiving data on the network.
  *
- * @note It is RECOMMENDED that the transport receive implementation
- * does NOT block when requested to read a single byte. A single byte
- * read request can be made by the caller to check whether there is a
- * new frame available on the network for reading.
- * However, the receive implementation MAY block for a timeout period when
- * it is requested to read more than 1 byte. This is because once the caller
- * is aware that a new frame is available to read on the network, then
- * the likelihood of reading more than one byte over the network becomes high.
+ * @note It is HIGHLY RECOMMENDED that the transport receive 
+ * implementation does NOT block when requested to read bytes.
+ * CoreMQTT will continue to request bytes from the transport
+ * interface until it has received all bytes necessary for a MQTT packet.
  *
  * @param[in] pNetworkContext Implementation-defined network context.
  * @param[in] pBuffer Buffer to receive the data into.